Hückel Theory Hückel’s Molecular Orbital Theory By Sean Hanley.
Fundamentals of Magnetism - CBPFieeemag/lectures/Jander_I.pdf · Orbital Magnetic Moment •For an...
Transcript of Fundamentals of Magnetism - CBPFieeemag/lectures/Jander_I.pdf · Orbital Magnetic Moment •For an...
Fundamentals of Magnetism Albrecht Jander
Oregon State University
Part I H M B χ micro Part II M(H)
Magnetic Field from Current in a Wire
Amperersquos Circuital Law
119867 ∙ 119889119897 = 119868
Biot-Savart Law
119867 = 1198682120587120587
[Am]
119889119867 =119868119889119897 times 119877
4120587 1198772
I
H
c
c dl
dl
R r
c
Andreacute-Marie Ampegravere (1775ndash1836)
Jean-Baptiste Biot (1774 ndash1862)
Feacutelix Savart (1791 ndash 1841)
Magnetic Field from Current Loop
Use Biot-Savart Law
119867 = 1198682120587
[Am] 119889119867 =
119868119889119897 times 119877
4120587 1198772
I
H
r
In the center
Magnetic Field in a Long Solenoid
119867 = 119873119868119871
[Am]
I
H
Inside field is uniform with
I
L
N turns
JS
119867 = 119869119878 [Am]
Magnetic Field from ldquoSmallrdquo Loop (Dipole)
I
H
r
Magnetic Field from Small Loop (Dipole)
H
For R gtgt r
119867 =119868119868
41205871198773 2119955 cos 120579 + 120637sin (120579)
R
θ
119898 = 119868119868 [Am2] Magnetic (dipole) moment
[Am]
Compare to Electric dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Magnetic Poles and Dipoles
119867 =119902119898
41205871198772 [Am]
+ qm
Magnetic field from a magnetic ldquomonopolerdquo
[Am] 119902119898
+ q
119863 =119902
41205871198772
Electric charge Magnetic charge or ldquopolerdquo
d
+ qm
qm
[Am] 119902119898
Magnetic Field of a Dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Orbital Magnetic Moment
bullFor an electron with charge qe orbiting at a radius R with frequency f the Orbital Magnetic Moment is
bull It also has an Orbital Angular Momentum
bull Note
e-
2RfqIAm e πminus==
RRfmvRmL ee π2==
ratioicgyromagnetmq
Lm
e
e =minus
=2
bullElectrons orbiting a nucleus are like a circulating current producing a magnetic field
[Am2]
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetic Field from Current in a Wire
Amperersquos Circuital Law
119867 ∙ 119889119897 = 119868
Biot-Savart Law
119867 = 1198682120587120587
[Am]
119889119867 =119868119889119897 times 119877
4120587 1198772
I
H
c
c dl
dl
R r
c
Andreacute-Marie Ampegravere (1775ndash1836)
Jean-Baptiste Biot (1774 ndash1862)
Feacutelix Savart (1791 ndash 1841)
Magnetic Field from Current Loop
Use Biot-Savart Law
119867 = 1198682120587
[Am] 119889119867 =
119868119889119897 times 119877
4120587 1198772
I
H
r
In the center
Magnetic Field in a Long Solenoid
119867 = 119873119868119871
[Am]
I
H
Inside field is uniform with
I
L
N turns
JS
119867 = 119869119878 [Am]
Magnetic Field from ldquoSmallrdquo Loop (Dipole)
I
H
r
Magnetic Field from Small Loop (Dipole)
H
For R gtgt r
119867 =119868119868
41205871198773 2119955 cos 120579 + 120637sin (120579)
R
θ
119898 = 119868119868 [Am2] Magnetic (dipole) moment
[Am]
Compare to Electric dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Magnetic Poles and Dipoles
119867 =119902119898
41205871198772 [Am]
+ qm
Magnetic field from a magnetic ldquomonopolerdquo
[Am] 119902119898
+ q
119863 =119902
41205871198772
Electric charge Magnetic charge or ldquopolerdquo
d
+ qm
qm
[Am] 119902119898
Magnetic Field of a Dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Orbital Magnetic Moment
bullFor an electron with charge qe orbiting at a radius R with frequency f the Orbital Magnetic Moment is
bull It also has an Orbital Angular Momentum
bull Note
e-
2RfqIAm e πminus==
RRfmvRmL ee π2==
ratioicgyromagnetmq
Lm
e
e =minus
=2
bullElectrons orbiting a nucleus are like a circulating current producing a magnetic field
[Am2]
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetic Field from Current Loop
Use Biot-Savart Law
119867 = 1198682120587
[Am] 119889119867 =
119868119889119897 times 119877
4120587 1198772
I
H
r
In the center
Magnetic Field in a Long Solenoid
119867 = 119873119868119871
[Am]
I
H
Inside field is uniform with
I
L
N turns
JS
119867 = 119869119878 [Am]
Magnetic Field from ldquoSmallrdquo Loop (Dipole)
I
H
r
Magnetic Field from Small Loop (Dipole)
H
For R gtgt r
119867 =119868119868
41205871198773 2119955 cos 120579 + 120637sin (120579)
R
θ
119898 = 119868119868 [Am2] Magnetic (dipole) moment
[Am]
Compare to Electric dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Magnetic Poles and Dipoles
119867 =119902119898
41205871198772 [Am]
+ qm
Magnetic field from a magnetic ldquomonopolerdquo
[Am] 119902119898
+ q
119863 =119902
41205871198772
Electric charge Magnetic charge or ldquopolerdquo
d
+ qm
qm
[Am] 119902119898
Magnetic Field of a Dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Orbital Magnetic Moment
bullFor an electron with charge qe orbiting at a radius R with frequency f the Orbital Magnetic Moment is
bull It also has an Orbital Angular Momentum
bull Note
e-
2RfqIAm e πminus==
RRfmvRmL ee π2==
ratioicgyromagnetmq
Lm
e
e =minus
=2
bullElectrons orbiting a nucleus are like a circulating current producing a magnetic field
[Am2]
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetic Field in a Long Solenoid
119867 = 119873119868119871
[Am]
I
H
Inside field is uniform with
I
L
N turns
JS
119867 = 119869119878 [Am]
Magnetic Field from ldquoSmallrdquo Loop (Dipole)
I
H
r
Magnetic Field from Small Loop (Dipole)
H
For R gtgt r
119867 =119868119868
41205871198773 2119955 cos 120579 + 120637sin (120579)
R
θ
119898 = 119868119868 [Am2] Magnetic (dipole) moment
[Am]
Compare to Electric dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Magnetic Poles and Dipoles
119867 =119902119898
41205871198772 [Am]
+ qm
Magnetic field from a magnetic ldquomonopolerdquo
[Am] 119902119898
+ q
119863 =119902
41205871198772
Electric charge Magnetic charge or ldquopolerdquo
d
+ qm
qm
[Am] 119902119898
Magnetic Field of a Dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Orbital Magnetic Moment
bullFor an electron with charge qe orbiting at a radius R with frequency f the Orbital Magnetic Moment is
bull It also has an Orbital Angular Momentum
bull Note
e-
2RfqIAm e πminus==
RRfmvRmL ee π2==
ratioicgyromagnetmq
Lm
e
e =minus
=2
bullElectrons orbiting a nucleus are like a circulating current producing a magnetic field
[Am2]
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetic Field from ldquoSmallrdquo Loop (Dipole)
I
H
r
Magnetic Field from Small Loop (Dipole)
H
For R gtgt r
119867 =119868119868
41205871198773 2119955 cos 120579 + 120637sin (120579)
R
θ
119898 = 119868119868 [Am2] Magnetic (dipole) moment
[Am]
Compare to Electric dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Magnetic Poles and Dipoles
119867 =119902119898
41205871198772 [Am]
+ qm
Magnetic field from a magnetic ldquomonopolerdquo
[Am] 119902119898
+ q
119863 =119902
41205871198772
Electric charge Magnetic charge or ldquopolerdquo
d
+ qm
qm
[Am] 119902119898
Magnetic Field of a Dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Orbital Magnetic Moment
bullFor an electron with charge qe orbiting at a radius R with frequency f the Orbital Magnetic Moment is
bull It also has an Orbital Angular Momentum
bull Note
e-
2RfqIAm e πminus==
RRfmvRmL ee π2==
ratioicgyromagnetmq
Lm
e
e =minus
=2
bullElectrons orbiting a nucleus are like a circulating current producing a magnetic field
[Am2]
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetic Field from Small Loop (Dipole)
H
For R gtgt r
119867 =119868119868
41205871198773 2119955 cos 120579 + 120637sin (120579)
R
θ
119898 = 119868119868 [Am2] Magnetic (dipole) moment
[Am]
Compare to Electric dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Magnetic Poles and Dipoles
119867 =119902119898
41205871198772 [Am]
+ qm
Magnetic field from a magnetic ldquomonopolerdquo
[Am] 119902119898
+ q
119863 =119902
41205871198772
Electric charge Magnetic charge or ldquopolerdquo
d
+ qm
qm
[Am] 119902119898
Magnetic Field of a Dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Orbital Magnetic Moment
bullFor an electron with charge qe orbiting at a radius R with frequency f the Orbital Magnetic Moment is
bull It also has an Orbital Angular Momentum
bull Note
e-
2RfqIAm e πminus==
RRfmvRmL ee π2==
ratioicgyromagnetmq
Lm
e
e =minus
=2
bullElectrons orbiting a nucleus are like a circulating current producing a magnetic field
[Am2]
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Magnetic Poles and Dipoles
119867 =119902119898
41205871198772 [Am]
+ qm
Magnetic field from a magnetic ldquomonopolerdquo
[Am] 119902119898
+ q
119863 =119902
41205871198772
Electric charge Magnetic charge or ldquopolerdquo
d
+ qm
qm
[Am] 119902119898
Magnetic Field of a Dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Orbital Magnetic Moment
bullFor an electron with charge qe orbiting at a radius R with frequency f the Orbital Magnetic Moment is
bull It also has an Orbital Angular Momentum
bull Note
e-
2RfqIAm e πminus==
RRfmvRmL ee π2==
ratioicgyromagnetmq
Lm
e
e =minus
=2
bullElectrons orbiting a nucleus are like a circulating current producing a magnetic field
[Am2]
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetic Poles and Dipoles
119867 =119902119898
41205871198772 [Am]
+ qm
Magnetic field from a magnetic ldquomonopolerdquo
[Am] 119902119898
+ q
119863 =119902
41205871198772
Electric charge Magnetic charge or ldquopolerdquo
d
+ qm
qm
[Am] 119902119898
Magnetic Field of a Dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Orbital Magnetic Moment
bullFor an electron with charge qe orbiting at a radius R with frequency f the Orbital Magnetic Moment is
bull It also has an Orbital Angular Momentum
bull Note
e-
2RfqIAm e πminus==
RRfmvRmL ee π2==
ratioicgyromagnetmq
Lm
e
e =minus
=2
bullElectrons orbiting a nucleus are like a circulating current producing a magnetic field
[Am2]
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
d
+ qm
qm
[Am] 119902119898
Magnetic Field of a Dipole
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Orbital Magnetic Moment
bullFor an electron with charge qe orbiting at a radius R with frequency f the Orbital Magnetic Moment is
bull It also has an Orbital Angular Momentum
bull Note
e-
2RfqIAm e πminus==
RRfmvRmL ee π2==
ratioicgyromagnetmq
Lm
e
e =minus
=2
bullElectrons orbiting a nucleus are like a circulating current producing a magnetic field
[Am2]
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetic Field of a Dipole
H
For R gtgt r
119867 =11990211989811988941205871198773 2 cos 120579 + 120579sin (120579)
R
θ
119898 = 119902119898119889 [Am2] Magnetic (dipole) moment
[Am]
[Am] 119902119898
Orbital Magnetic Moment
bullFor an electron with charge qe orbiting at a radius R with frequency f the Orbital Magnetic Moment is
bull It also has an Orbital Angular Momentum
bull Note
e-
2RfqIAm e πminus==
RRfmvRmL ee π2==
ratioicgyromagnetmq
Lm
e
e =minus
=2
bullElectrons orbiting a nucleus are like a circulating current producing a magnetic field
[Am2]
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Orbital Magnetic Moment
bullFor an electron with charge qe orbiting at a radius R with frequency f the Orbital Magnetic Moment is
bull It also has an Orbital Angular Momentum
bull Note
e-
2RfqIAm e πminus==
RRfmvRmL ee π2==
ratioicgyromagnetmq
Lm
e
e =minus
=2
bullElectrons orbiting a nucleus are like a circulating current producing a magnetic field
[Am2]
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
bullBohr Model orbit must be integer number of wavelengths
bull Thus the orbital magnetic moment is quantized
bull Magnetic moment restricted to multiples of
vmh
edB =λ
Bohr model of the atom
RfmhN
vmhNNR
eedB π
λπ2
2 ===
e
e
e
ee m
qNmqhNRfqm
2222
==minus=π
π
][10274292
224 Ammq
e
eB
minustimes==micro
Bohr Magneton
bullDeBroglie wavelength is
e-
dBλ
R
Louis de Broglie (1892-1987)
Orbital Moment is Quantized
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Spin
Pauli and Bohr contemplate the ldquospinrdquo of a tippy-top
bull Spin is a property of subatomic particles (just like charge or mass)
bull A particle with spin has a magnetic dipole moment and angular momentum
bull Spin may be thought of conceptually as arising from a spinning sphere of charge (However note that neutrons also have spin but no charge)
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Electron Spin bull When measured in a particular direction the
measured angular momentum of an electron is
2
plusmn=zL
bull When measured in a particular direction the measured magnetic moment of an electron is
Be
ezz m
qsm microplusmn==
e
e
mq
Lm minus
=bull Note
e
e
mq
Lm minus
=e
e
mq
Lm
2minus
=
Compare Spin Orbital
Bzm microplusmn= Bz Nm micro=bull We say ldquospin uprdquo and ldquospin downrdquo
e
e
mqg
Lm
2minus
= 1=g2=g
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Stern-Gerlach Experiment - 1922
Walter Gerlach (1889-1979)
Otto Stern (1888-1969)
Demonstrated that magnetic moment is quantized with plusmnmicroB
Walther Gerlach Otto Stern (1922) Das magnetische Moment des Silberatoms Zeitschrift fuumlr Physik A Hadrons and Nuclei 9
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Stern-Gerlach Experiment
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Quantum Numbers of Electron Orbitals bullElectrons bound to a nucleus move in orbits identified by quantum numbers (from solution of Schroumldingers equation)
n 1hellip principal quantum number identifies the ldquoshellrdquo l 0n-1 angular momentum q type of orbital eg spdf ml -ll magnetic quantum number ms +frac12 or -frac12 spin quantum number
For example the electron orbiting the hydrogen nucleus (in the ground state) has
n=1 l=0 ml=0 ms=+frac12
In spectroscopic notation 1s1
Spectroscopic notation l=0 s l=1 p l=2 d l=3 f n l of electrons in orbital 1s22s2
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Spin and Orbital Magnetic Moment bull Total orbital magnetic moment (sum over all electron orbitals)
bull Total spin magnetic moment
Eg Iron
1s22s22p63s23p63d64s2
How to fill remaining d orbitals (l=2) 6 electrons for 10 spots
full orbitals no net moment
sum= lmm Borbitaltot micro_
sum= sBspintot mm micro2_
ml=-2 ml=-1 ml=0 ml=+1 ml=+2 ms=+frac12 ms=-frac12
BspintotBorbitaltot mm micromicro 42 __ ==
Hundrsquos rules
Maximize Σms
Then maximize Σml
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetization M
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898
What is H here
M Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Equivalent Loop Currents
What is H here
119868
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
Magnetic moment per unit volume
[Am] 119872 ≝119898119900119900119900
119907119907119897= 119898119886119886119900119898119889
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Equivalent Surface Current
Equivalent surface current
[Am] 119869119878 = 119872 times 119899
What is H here
119868
M 119899
JS [Am]
Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = I119868
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetic Pole Model
Atomic magnetic moment
Magnetic moment per unit volume
[Am] 119872 ≝119898
119907119907119897
What is H here
M Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Equivalent Surface Pole Density
Magnetic pole density
[Am] 120588119898119898 = 119872 ∙ 119899
M
120588119898119898 =119902119898
119886119903119886119886
Surface charge density
[Am]
[m2]
Atomic magnetic moment Atomic magnetic moment
[Am2]
Atomic density
[1m3]
119898119886119886119907119898 = 119902119898119889
Object magnetic moment
119898119900119900119900 = sum119898119886119886119900119898 [Am2]
119889 =119873
119907119907119897
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
JS =106 [Am]
I = 20000 [A]
m = IA = 14 [Am2]
A ≃ 7middot10-4 [m2]
JS
A
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example NdFeB Cylinder
M
M =106 [Am]
vol ≃ 14middot10-6
2 cm
3 cm
[m3]
m = 14 [Am2]
ρms =106 [Am]
qm = 700 [Am]
m = qmd = 14 [Am2]
A ≃ 7middot10-4 [m2]
ρms
d =2middot10-2 [m]
+ + + + + + + + + + + + +
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is the same external to magnetic material
Hint we are ldquofarrdquo away from the dipoles
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example NdFeB Cylinder
M
+ + + + + + + + + + + + +
Result is different inside the magnetic material
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
The Constitutive Relation
119913 = 120641120782(119919 + 119924)
Note in vacuum M is zero
B = Magnetic flux density [ Tesla ] H = Magnetic field ldquoMagnetizing forcerdquo [Am] M = Magnetization [Am] micro0 = Magnetic constant ldquoPermeability of free spacerdquo [Tesla-mA] [Henrym] [NA2]
119913 = 120641120782119919
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
What is microo
The ampere is that constant current which if maintained in two straight parallel conductors of infinite length of negligible circular cross section and placed 1 meter apart in vacuum would produce between these conductors a force equal to 2times10minus7 newton per meter of length
micro0 comes from the SI definition of the Ampere
I1
I2
F
119913 = 120641120782119919 =120641120782119920120783 120784120645119955
119917 = 119920120784119923 times 119913 B
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Maxwellrsquos Equations (Magnetostatics)
120513 ∙ 119913 = 120782
120513 times 119919 =
119913 ∙ 119941119956 = 120782
119919 ∙ 119941119949 = 119920
Differential form Integral form
119913 = 120641120782(119919 + 119924)
120513 ∙ 119913 = 120641120782(120513 ∙ 119919 + 120513 ∙ 119924) 120513 ∙ 119919 = minus120513 ∙ 119924 = 120646119950 [Am2]
With
Magnetic charge density ie magnetic chargevolume
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example NdFeB Cylinder
+ + + + + + + + + + + + +
B H 119913 = 120641120782(119919 + 119924)
M
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Boundary Conditions
B1 B2
The perpendicular component of B is continuous across a boundary
H1|| H2||
The transverse component of H is continuous across a boundary (unless there is a true current on the boundary)
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Demagnetizing Fields
+ + + + + + + + + + + + +
Hd
119919119941 prop 119924
M
119919119941 = minus119925119924 Demagnetizing Factor
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Demagnetizing Factors Special Cases 119919119941 = minus119925119924 119925119961 + 119925119962 + 119925119963 = 120783
Sphere
119925119961 = 119925119962 = 119925119963 =120783120785
Long Rod
119925119961 = 119925119962 =120783120784
119925119963 = 120782
Thin Sheet
119925119961 = 119925119962 = 120782 119925119963 = 120783
x
y
z
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Demagnetizing Factors
119919119941 = minus119925119924
ldquoDemagrdquo fields in ellipsoids of revolution are uniform
119925119961 + 119925119962 + 119925119963 = 120783
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example Ba-Ferrite Sphere
119919119941 = minus119925119924
119925119961 = 119925119962 = 119925119963 =120783120785
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120782 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120782120782 ) [kAm]
119913 = 120782 120783120784120783 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119961 = 119925119962 = 120782 120786120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120788 120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120790120784 120783 ) [kAm]
119913 = 120782 120783120782120786 [Tesla]
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example Ba-Ferrite Ellipsoid
119919119941 = minus119925119924
119925119963 = 120782 120783
Barrium Ferrite
119924~120783120783120782 [kAm]
119919119941 = minus120783120783 [kAm]
M H B
119913 = 120641120782(119919 + 119924)
119913 = 120641120782(120783120785120783 ) [kAm]
119913 = 120782 120783120788 [Tesla]
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Susceptibility and Permeability Ideal permanent magnet
Ideal linear soft magnetic material
Real useful magnetic material
H
M
H
M
H
M
119924 = 120652119919 Susceptibility [unitless]
119913 = 120641120782(119919 + 120652119919)
119913 = 120641120782(120783 + 120652)119919
119913 = 120641120782120641119955119919 Rel Permeability
[unitless]
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example Long Rod in a Long Solenoid
119867 = 119873119868119871
= 1 [kAm]
119872 = 120594119867 = 120594 119873119868119871
= 999 [kAm]
I =1 A NL = 1000m
120583120587 = 1000 120594 = 999
119861 = 1205830 119867 + 119872 = 1205830(1000kAm)= 125 [Tesla]
or
119861 = 1205830120583120587119867= 125 [Tesla]
119861 = 1205830119867= 000125 [Tesla]
Note without the rod
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example Soft Magnetic Ball in a Field
M Hd B
119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
Hext
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example Soft Magnetic Ball in a Field
B 119924 = 120652119919 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119925119924
119924 =120652
120783 + 119925120652119919119942119961119942 120652119942119942119942 =
120652120783 + 119925120652
lt 120785
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Example Thin Film in a Field
119924 = 120652119919119946119946119956119946119941119942 = 120652 119919119942119961119942 + 119919119941 = 120652 119919119942119961119942 minus 119924
Hext
119924 =120652
120783 + 120652119919119942119961119942
119919119946119946119956119946119941119942 =120783
120783 + 120652119919119942119961119942 119913119946119946119956119946119941119942 = 119861119942119961119942
Why
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Torque and Zeeman Energy
+ + + + + + + + + + + + +
F
F
M B = 119902119898119861
119983 = 119898 times 119861
Force
Torque
Energy
119864 = minus119898 ∙ 119861
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Self Energy and Shape Anisotropy
119864 = 12 1205830119872 ∙ 119867119889119907
119907119900119900
M Hd M
Hd Higher energy Lower energy
ldquoShape Anisotropyrdquo
119864 = 121205830119872119898
2 119873119909 minus 119873119884 1199041199041198992(120579)
θ
E
0 180 360
M Easy axis
Har
d ax
is
Easy Easy
Hard Hard
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetic Circuits
N turns
I 119919 ∙ 119941119949 = 119925119920
Assuming flux is uniform and contained inside permeable material
119913 = 120641120782120641119955119919 =120659119912
areaA
119925119920 = 120659120659
120659 =119949
120641119912 Magneto-motive force ldquoMMFrdquo
Flux
Reluctance
path length l
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Magnetic Circuits
NI 120659119944119944119944 120659120785
120659120783 120659120784
120659120786 120659120783
120659119944119944119944
Solve using electric circuit theory
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Units Confusion
119913 = 120641120782 119919 + 119924 119913 = 119919 + 120786120645119924
B [Gauss] H [Oersted] M [emucc] 4πM [Gauss]
B [Tesla] H [Am] M [Am]
119913 ∙ 119919 [dynecm3] 119913 ∙ 119919 [Jm3]
119925119961 + 119925119962 + 119925119963 = 120783 119925119961 + 119925119962 + 119925119963 = 120786120645
CGS Units SI Units
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-
Books on Magnetism
BD Cullity Introduction to Magnetic Materials Wiley-IEEE Press 2010 (revised version with CD Graham) M Coey Magnetism and Magnetic Materials Cambridge University Press 2010 S Chikazumi Physics of Magnetism John Wiley and Sons 1984 RC OrsquoHandley Modern Magnetic Materials John Wiley amp Sons 2000 RL Comstock Introduction to Magnetism and Magnetic Recording John Wiley amp Sons 1999 D Jiles Introduction to Magnetism and Magnetic Materials CRC Press 1998 Bozorth Ferromagnetism1951 (reprinted by IEEE Press 1993)
- Fundamentals of Magnetism
- Magnetic Field from Current in a Wire
- Magnetic Field from Current Loop
- Magnetic Field in a Long Solenoid
- Magnetic Field from ldquoSmallrdquo Loop (Dipole)
- Magnetic Field from Small Loop (Dipole)
- Magnetic Field of a Dipole
- Magnetic Poles and Dipoles
- Magnetic Field of a Dipole
- Magnetic Field of a Dipole
- Orbital Magnetic Moment
- Orbital Moment is Quantized
- Spin
- Electron Spin
- Stern-Gerlach Experiment - 1922
- Stern-Gerlach Experiment
- Quantum Numbers of Electron Orbitals
- Spin and Orbital Magnetic Moment
- Slide Number 26
- Magnetization M
- Equivalent Loop Currents
- Equivalent Surface Current
- Magnetic Pole Model
- Equivalent Surface Pole Density
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- Example NdFeB Cylinder
- The Constitutive Relation
- What is mo
- Maxwellrsquos Equations (Magnetostatics)
- Example NdFeB Cylinder
- Boundary Conditions
- Demagnetizing Fields
- Demagnetizing Factors Special Cases
- Demagnetizing Factors
- Example Ba-Ferrite Sphere
- Example Ba-Ferrite Ellipsoid
- Example Ba-Ferrite Ellipsoid
- Susceptibility and Permeability
- Example Long Rod in a Long Solenoid
- Example Soft Magnetic Ball in a Field
- Example Soft Magnetic Ball in a Field
- Example Thin Film in a Field
- Torque and Zeeman Energy
- Self Energy and Shape Anisotropy
- Magnetic Circuits
- Magnetic Circuits
- Units Confusion
- Books on Magnetism
-