Antiphase magnetic proximity effect in perovskite ... · 1 LNS, ETHZ & PSI 2 MPI-FKF, Stuttgart 3...
Transcript of Antiphase magnetic proximity effect in perovskite ... · 1 LNS, ETHZ & PSI 2 MPI-FKF, Stuttgart 3...
Laboratory for Neutronen ScatteringETH Zurich & Paul Scherrer Institute
Jochen Stahn
Antiphase magnetic proximity effect
in perovskite
superconductor / ferromagnet multilayers
SFB 491 Seminar 23. 02. 2006Ruhr-Universitat Bochum
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 12π λ2δ(
z)·1
06z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
0
-1
-2
-3
0.01 0.02 0.03 0.04 0.05 0.06 0.07
qz/A−1
reflec
tivi
tylo
g[R
(qz)]
|+〉
|−〉
above TCurie
question: What is the magnetic induction
(profile) in HTSC /FM
multilayers?
method: polarised neutron reflectometry
allows for the determination of
ρ(z) and B‖(z)
answers: FM layers magnetised parallel
net magnetic moment in SC
at the interfaces, antiparallel
to FM magnetisation
SC creates and aligns domain
walls in FM
essence
1
1 LNS, ETHZ & PSI2 MPI-FKF, Stuttgart3 Universitat Fribourg
4 RUB / ILL5 FZ Julich
samples
G. Cristiani 2
HU. Habermeier 2
J. Hoppler 1
S. Pekarek 1
C. Niedermayer 1
E. Kenzinger 5
J. Chakhalian 2
analysis measurements
T. Gutberlet 1
U. Rucker 5
M. Wolff 4
interpretation
C. Bernhard 3
B. Keimer 2
cooperators:
2
general idea: the close contact of materials with different (alternative)
properties might lead to new phenomena
e.g. – interface of SrTiO3/LaTiO3 (insulators) is metallic
a multilayer reduces the dimension and forces the interaction
coupling phenomena might show up
e.g. – RKKY-interaction
– collosal magnetoresistance
– changed characteristic temperatures
present case: multilayers of a FM with a HTSC (both metals) seem to
show an metal/insulator transition in ellipsometry transition
for small periods — but stay superconducting / magnetic
so: what happens with the magnetisation and the
superconduction order parameter?
interfaces and layered systems “new physics” and “spintronics”?
3
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 12π λ2δ(
z)·1
06z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
0
-1
-2
-3
0.01 0.02 0.03 0.04 0.05 0.06 0.07
qz/A−1
reflec
tivi
tylo
g[R
(qz)]
|+〉
|−〉
above TCurie
question: What is the magnetic induction
(profile) in HTSC /FM
multilayers?
method: polarised neutron reflectometry
allows for the determination of
ρ(z) and B‖(z)
answers: FM layers magnetised parallel
net magnetic moment in SC
at the interfaces, antiparallel
to FM magnetisation
SC creates and aligns domain
walls in FM
overview
4
0 20 40 60 80 100 120 1400
10
20
30
40
100
150
200
Tc
Inte
rne
s M
ag
ne
tfeld
(G
)Temperatur (K)
Im Supraleiter Im Ferromagneten
Niederenergetische Myonen
0 50 100 150 2000.0
2.0x10-5
4.0x10-5
6.0x10-5
8.0x10-5
1.0x10-4
0.1 T 0.5 T 5 T
Mom
ent [
emu]
Temperature [K]
spring 2003:
C. Niedermayer presents nice µSR and
magnetisation measurements at PSI
enhanced magnetism below Tc
coexistence of FM and SC in RuSrCuGdO
→ competitive order parameters
artificial multilayers to investigate
– interaction of FM and SC at the interfaces and
– coupling through the layer
motivation / history:
5
0 20 40 60 80 100 120 1400
10
20
30
40
100
150
200
Tc
Inte
rne
s M
ag
ne
tfeld
(G
)Temperatur (K)
Im Supraleiter Im Ferromagneten
Niederenergetische Myonen
0 50 100 150 2000.0
2.0x10-5
4.0x10-5
6.0x10-5
8.0x10-5
1.0x10-4
0.1 T 0.5 T 5 T
Mom
ent [
emu]
Temperature [K]
spring 2003:
C. Niedermayer presents nice µSR and
magnetisation measurements at PSI
enhanced magnetism below Tc
method of choice
(for a neutron scatterer):
neutrons!
in particular polarised n-reflectometry
motivation / history:
6
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 12π λ2δ(
z)·1
06z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
0
-1
-2
-3
0.01 0.02 0.03 0.04 0.05 0.06 0.07
qz/A−1
reflec
tivi
tylo
g[R
(qz)]
|+〉
|−〉
above TCurie
question: What is the magnetic induction
(profile) in HTSC /FM
multilayers?
method: polarised neutron reflectometry
allows for the determination of
ρ(z) and B‖(z)
answers: FM layers magnetised parallel
net magnetic moment in SC
at the interfaces, antiparallel
to FM magnetisation
SC creates and aligns domain
walls in FM
overview
7
qz
q = kf − ki
ki kfz
V (z)
period
substrate
|+〉
|−〉
SCFM
ki kf
qzωω R
(ω)
layer thickness ratio 1:1⇒ extinction of evenBragg-peaks
interference of beams reflected from parallel interfaces
periodic structure ⇒ Bragg-condition for constructive interference
scattering potential:
V = Vnuc ± Vmag
= Vnuc + µB‖
reflectometry
8
YB
a 2Cu 3
O7
La 2
/3Ca 1
/3M
nO3
La
Ba
Y
Mn
Cu
O
materials: HTSC YBCO YBa2Cu3O7
FM LCMO La2/3Ca1/3MnO3
substr. STO SrTiO3
size: 10 × 10 mm2
(instead of 5 × 5 mm2)
produced: by Pulsed Laser Deposition
period: 200 A to 500 A
5 to 16 periods
ratios: 1 : 1 and 1 : 2
to cause extinction
non-rough interfaces
(otherwise used to tune Tc)
reflectometry tailored samples
9
sample holderwith absorber
closed cycle refrigerator8 K < T < 300 K
Helmholtz coilsH ≤ 1000 Oevol: 40 × 40 × 40 mm3
translation stages for alignment
ω-rotation stage
reflectometry sample environment (at SINQ):
10
detectordiaphragm
sample &environment
flipper & polariser
monochromator
ω2θ
qz
ω
R(ω
)
0
-1
-2
-3
0.01 0.02 0.03 0.04 0.05 0.06 0.07
qz/A−1
reflec
tivi
tylo
g[R
(qz)]
|+〉
|−〉
above TCurie
exam
ple
:
Mor
pheu
s@
SIN
Q
reflectometry
11
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 12π λ2δ(
z)·1
06z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
0
-1
-2
-3
0.01 0.02 0.03 0.04 0.05 0.06 0.07
qz/A−1
reflec
tivi
tylo
g[R
(qz)]
|+〉
|−〉
above TCurie
question: What is the magnetic induction
(profile) in HTSC /FM
multilayers?
method: polarised neutron reflectometry
allows for the determination of
ρ(z) and B‖(z)
answers: FM layers magnetised parallel
net magnetic moment in SC
at the interfaces, antiparallel
to FM magnetisation
SC creates and aligns domain
walls in FM
overview
12
0
-1
-2
-3
0.01 0.02 0.03 0.04 0.05 0.06 0.07
reflec
tivi
tylo
g[R
(qz)]
1st
2nd
3rd
above TCurie
|+〉 , 10 K
|−〉 , 10 K
��
��
��
��
��
���
��
��
��
��
��
��
��
���7
�����������������������
6
splitting of the edge of total reflection⇒ changed potential of the surface
no half-order Bragg-peak⇒ parallel alignment of B in the FM layers
intensity variation of the 1st Bragg-peak⇒ changed potential in the FM layersB‖ can be determined
appearance of a 2nd order Bragg-peak⇒ B‖(z) and Vnuc(z) have different symmetry
H = 100 Oe
field cooled
T = 10, 300 K
reflectometry direct interpretation
13
LCMOYBCO
(z)B
cosh-functions
off-sets with
constant B
simulations performed with EDXR by Petr Mikulık (no fitting)
bilayer structure has been broken down to
some 100 sublayers to pay respect to B(z).
analytic expressions for B(z):
decrease of layer thickness towards the borders taken into account
reflectometry simulations
14
zδ
δ(z)
zδ
δ(z)
|−〉 |+〉
LCMO
YBCO
STO
0
-1
-2
-3
reflec
tivi
tylo
g[R
(qz)]
1st
2nd
3rd|+〉
|−〉
above TCurie
cal c
ul a
t ed
-4
-3
-2
-1
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07
qz/A−1
reflec
tivi
tylo
g[R
(qz)]
|+〉
|−〉
above TCurie
sample:
[YBCO(150 A)/LCMO(140 A)]5
reflectometry simulation specular, polarised
15
zδ
δ(z)
zδ
δ(z)
|−〉 |+〉
LCMO
YBCO
STO
0
-1
-2
-3
reflec
tivi
tylo
g[R
(qz)]
1st
2nd
3rd|+〉
|−〉
above TCurie
cal c
ul a
t ed
-4
-3
-2
-1
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07
qz/A−1
reflec
tivi
tylo
g[R
(qz)]
|+〉
|−〉
above TCurie
too
si m
pl e
!
δmag(z) 6= δnuc(z) ×
0 for YBCO
const for LCMO
sample:
[YBCO(150 A)/LCMO(140 A)]5
reflectometry specular, polarised
16
0
-1
-2
-3
reflec
tivi
tylo
g[R
(qz)]
1st
2nd
3rd|+〉
|−〉
above TCurie
cal c
ul a
t ed
-4
-3
-2
-1
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07
reflec
tivi
tylo
g[R
(qz)]
qz/A−1
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
2π λ2δ(
z)·1
06
z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
sharp contrast at the interface
exponential decay into YBCO
AFM exponential decay into YBCO
penetration into YBCO
magnetically dead layer in LCMO
modelling magnetic profile at the interfaces
17
0
-1
-2
-3
reflec
tivi
tylo
g[R
(qz)]
1st
2nd
3rd|+〉
|−〉
above TCurie
cal c
ul a
t ed
-4
-3
-2
-1
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07
reflec
tivi
tylo
g[R
(qz)]
qz/A−1
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
2π λ2δ(
z)·1
06
z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
sharp contrast at the interface
exponential decay into YBCO
AFM exponential decay into YBCO
penetration into YBCO
magnetically dead layer in LCMO
modelling magnetic profile at the interfaces
18
0
-1
-2
-3
reflec
tivi
tylo
g[R
(qz)]
1st
2nd
3rd|+〉
|−〉
above TCurie
cal c
ul a
t ed
-4
-3
-2
-1
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07
reflec
tivi
tylo
g[R
(qz)]
qz/A−1
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
2π λ2δ(
z)·1
06
z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
sharp contrast at the interface
exponential decay into YBCO
AFM exponential decay into YBCO
penetration into YBCO
magnetically dead layer in LCMO
modelling magnetic profile at the interfaces
19
0
-1
-2
-3
reflec
tivi
tylo
g[R
(qz)]
1st
2nd
3rd|+〉
|−〉
above TCurie
cal c
ul a
t ed
-4
-3
-2
-1
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07
reflec
tivi
tylo
g[R
(qz)]
qz/A−1
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
2π λ2δ(
z)·1
06
z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
sharp contrast at the interface
exponential decay into YBCO
AFM exponential decay into YBCO
penetration into YBCO
magnetically dead layer in LCMO
modelling magnetic profile at the interfaces
20
0
-1
-2
-3
reflec
tivi
tylo
g[R
(qz)]
1st
2nd
3rd|+〉
|−〉
above TCurie
cal c
ul a
t ed
-4
-3
-2
-1
0
0.01 0.02 0.03 0.04 0.05 0.06 0.07
reflec
tivi
tylo
g[R
(qz)]
qz/A−1
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
2π λ2δ(
z)·1
06
z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
sharp contrast at the interface
exponential decay into YBCO
AFM exponential decay into YBCO
penetration into YBCO
magnetically dead layer in LCMO
modelling magnetic profile at the interfaces
21
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
2π λ2δ(
z)·1
06
z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
2π λ2δ(
z)·1
06
z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
PNR at RT and below TCurie and Tc
exclude all models besides
AFM-region within LCMO
charge-injection from YBCO leads to
a doping of LCMO and thus to an
AFM ground state
antiphase magnetic proximity
effect
AF coupling of Mn and Cu moments
through oxygen
or
Cooper pairs penetrate into LCMO
and are polarised
⇒ antiparallel magnetisation in YBCO
resume
22
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
2π λ2δ(
z)·1
06
z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 1
2π λ2δ(
z)·1
06
z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
PRB 69, 174504 (2004):
PNR at RT and below TCurie and Tc
exclude all models besides
AFM-region within LCMO
charge-injection from YBCO leads to
a doping of LCMO and thus to an
AFM ground state
resume
23
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
-1 -0.5 0 0.5 1
mag
net
isat
ion
10−
7A
m2
H/103 Oe
SQUID measurements by F. Treubel, Konstanz
T = 5 K
cooled in H = 100 Oe
coercitive field Hco ≈ ±400 Oe
exchange bias Heb ≈ −60 Oe
⇓
presence of an AFM coupling
at the FM-interface
but:
– magnetically dead layer might be an AFM
– B in YBCO might be an AFM with net magnetic moment
magnetometry
24
-4
-3
-2
-1
0
0.02 0.04 0.06 0.08 0.1
qz/A−1
log[
R(q
z)]
1st Bragg peak
2nd Bragg peak
200K
15K
0.5
1
1.5
2
2.5
3
0 50 100 150 200 250 300
T / K
R(T
)/R
(RT
)
1st Bragg peak
|+〉
|−〉2nd Bragg peak
|+〉
|−〉
Tc
T ′ TCurie
[YB
CO
(100
A)/
LCM
O(1
00A
)]7
[YB
CO
(200
A)/
LCM
O(2
00A
)]8
TCurie (160 → 270 K)
onset of FM: changed contrast
T ′ (≈ 140 K)
formation of 2nd peaks
B(z) and Vnuc(z) differ
Tc (60 → 90 K)
onset of SC
T dependence of R(qz)
25
-4
-3
-2
-1
0
0.02 0.04 0.06 0.08 0.1
qz/A−1
log[
R(q
z)]
1st Bragg peak
2nd Bragg peak
200K
15K
0.5
1
1.5
2
2.5
3
0 50 100 150 200 250 300
T / K
R(T
)/R
(RT
)
1st Bragg peak
|+〉
|−〉2nd Bragg peak
|+〉
|−〉
Tc
T ′ TCurie
[YB
CO
(100
A)/
LCM
O(1
00A
)]7
[YB
CO
(200
A)/
LCM
O(2
00A
)]8
Te
mp
era
ture
An
tife
rro
ma
gn
etic Pseudogap
Fermi liquid
Non Fermi liquid
Doping level (holes per CuO )2
Underdoped Optimally doped Overdoped
Superconducting
?
�
T ∗
T ′TCurie
TCurie (160 → 270 K)
onset of FM: changed contrast
T ′ ≈ T ∗ (≈ 140 K)
formation of 2nd peaks
B(z) and Vnuc(z) differ
Tc (60 → 90 K)
onset of SC
T dependence of R(qz)
26
0
0.5
1
1.5
2
2.5
3
3.5
4
120 140 160 180 200
T/K
R(T
)/R
(RT
)
1st Bragg peak
|+〉
|−〉2nd Bragg peak
|+〉 + |−〉T ′
TCurie
0.5
1
1.5
2
2.5
3
0 50 100 150 200 250 300
T / K
R(T
)/R
(RT
)
1st Bragg peak
|+〉
|−〉2nd Bragg peak
|+〉
|−〉
Tc
T ′ TCurie
[YPB
CO
(200
A)/
LCM
O(2
00A
)]8
Y0.6Pr 0
.4B
a 2Cu 3
O7
[YB
CO
(200
A)/
LCM
O(2
00A
)]8
Te
mp
era
ture
An
tife
rro
ma
gn
etic Pseudogap
Fermi liquid
Non Fermi liquid
Doping level (holes per CuO )2
Underdoped Optimally doped Overdoped
Superconducting
?
����
T ′
T ∗
T ′TCurie
T ′ ≈ T ∗ varies with doping!
T dependence of R(qz)
27
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 12π λ2δ(
z)·1
06z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
0
-1
-2
-3
0.01 0.02 0.03 0.04 0.05 0.06 0.07
qz/A−1
reflec
tivi
tylo
g[R
(qz)]
|+〉
|−〉
above TCurie
question: What is the magnetic induction
(profile) in HTSC /FM
multilayers?
method: polarised neutron reflectometry
allows for the determination of
ρ(z) and B‖(z)
answers: FM layers magnetised parallel
net magnetic moment in SC
at the interfaces, antiparallel
to FM magnetisation
SC creates and aligns domain
walls in FM
overview
28
k0
kR,in−plane off−specular
kR,specular
kR,out−of−plane off−specular
qxz
qzqxyz
in our cases:resolution in x : ≈ 0.01◦
resolution in y : > 1◦
⇒ integrated over y
inclined surface facetts ⇒ ∆ω
height-variation ⇒ phase-shifts in kR
⇒ damping of R(qz > qc)
neutron scattering probes
a potential parallel to q
if q 6= q(z) also lateral
structure is accessible
here:
lateral and vertical
correlation length of
(magnetic) inhomogeneities
off-specular scattering principle
29
|+〉 , |+〉 |−〉 , |−〉 |+〉 , |−〉
10
0
10
20
0 10 2010
0
10
20
0 10 2010
0
10
20
0 10 20
10
0
10
20
0 10 2010
0
10
20
0 10 2010
0
10
20
0 10 20
10
0
10
20
0 10 2010
0
10
20
0 10 2010
0
10
20
0 10 20
exit
angl
eα
f/
mra
d
20
10
0
-10
20
10
0
-10
20
10
0
-10
angle of incidence αi / mrad0 10 20 0 10 20 0 10 20
ab
c
d
eXXXXXX
T=
200
KT
=16
0K
T=
130
K
No off-specular sheets at RT or 200 K⇒ no structural roughness detectable
Increase of the Bragg sheet at 1st
Bragg peak (d) below 160 K⇒ magnetic roughness, correlatedvertically
Appearance of sheets in the spin-flipchannel (e)⇒ magnetic moments not parallel tothe neutron spins
Interpretation (of all measurements):Magnetic domains of similar size (≈ 5to 10µm) are formed in the LCMOlayers. These are correlated throughYBCO over the whole stack.
off-specular scattering measured on HADAS@Julich
30
50100150200250
-1 -0.5 0 0.5 1
T/
K
qx / 10−4A−1
1
2
3
4
0 50 100 150 200 250
T / K
log[
R(q
z)]
integratd over qx
at peak positions
Tc
TCurie -4
-3
-2
-1
0
0.02 0.04 0.06 0.08 0.1
qz/A−1
reflec
tivi
tylo
g[R
(qz)]
1st Bragg peak
200 K
15 K
non-polarised, various T
sample: [YBCO(100 A)/LCMO(100 A)]7
magnetic domains shrink below Tc
from 10 µm to 5 µm when cooling
off-specular scattering ω-scans
31
TCurie
T ′
Tc
B‖
• all LCMO layers are magnetised parallel
• interface effect of B(z) of the order of10 A is measuredat Tc < T ′ ≈ 140 K < TCurie
– magnetic dead layer or antiphase
proximity effect
• simultaneous appearance of Bragg-sheets
– vertical correlation of magnetic domains
• increase of off-specular scattering belowTc
– shrinking of magnetic domains/ characteristic lengthscale
• correlation of domain size with T < Tc
and XMCD measurements support theantiphase proximity effect
conclusion:
32
-1
0
1
2
3
4
5
0 0.2 0.4 0.6 0.8 12π λ2δ(
z)·1
06z/d in one period
YBCO LCMO
|+〉
nuc
|−〉
mag
LCMO
0
-1
-2
-3
0.01 0.02 0.03 0.04 0.05 0.06 0.07
qz/A−1
reflec
tivi
tylo
g[R
(qz)]
|+〉
|−〉
above TCurie
question: What is the magnetic induction
(profile) in HTSC /FM
multilayers?
method: polarised neutron reflectometry
allows for the determination of
ρ(z) and B‖(z)
answers: FM layers magnetised parallel
net magnetic moment in SC
at the interfaces, antiparallel
to FM magnetisation
SC creates and aligns domain
walls in FM
essence
33
THE END