Recent progress in large tunnel magnetoresistance junctions

1. A little review of MTJs2. Heusler electrode TMR junctions

・ Relationship between degree of order and TMR ratio・ Temperature and bias dependences of TMR ratio

3. Applications of TMR junctions (Gilbert damping constant α)

T. Miyazaki1), Y. Sakuraba2), D.Watanabe3) S. Tsunegi3), M. Oogane3) and Y. Ando3)

March 6, 2008

1 WPI Advanced Institute for Materials Research Tohoku University, Sendai Japan. 2 Institute for Materials Research, Tohoku University，Sendai, Japan.3 Department of Applied Physic, Tohoku University, Sendai, Japan.

Aachen, Germany

JST-DFG Workshop on Nanoelectronics

1. A little review of MTJs

History of TMR research(Typical reports)

• Julliere (Phys. Lett., 54A,225(1975)) Gd-O• T.Miyazaki et al. (J.Magn.Magn.Mater.139,L231(1995)) Al-O• J.S.Moodera et al. (Phys.Rev.Lett., 74, 3273(1995)) Al-O•• S.Yuasa et al. (Jpn.J.Appl.Phys., 43, L588(2004)) MgO• S.S.P.Parkin et al. (Nature Materials, 3, 863(2004)) MgO•• Y.Sakuraba et al. (Appl.Phys.Lett., 88, 192508(2006)) Heusler

• N.Tezuka et al. (Appl.Phys. Lett.,89, 252508-1(2006)) Heusler

• T.Ishikawa et al. (Appl.Phys.Lett.,89,192505-1(2006)) Heusler

H (Oe)

M (arb.units)

-100 -50

50 100

(b)

-100 -50 0 50 100H (Oe)

0.006

0.007

0.008

0

20

10

RS

(a)R

(Ω)

ΔR

/ R

S(%

)at R. T.

Magnetoresistancecurve (a) and magnetic hysteresis loop (b) for Fe/Al2O3/Fe junction

Fe/Al2O3/Fe

T.Miyazaki and N.Tezuka, J.3M,

139,L2341(1995).

-200 -100 0 100 2000

100

200

300

MR

比( %

)

H ( Oe )

293 K

20 K

MR = 245 %

MR = 180 %

Yuasa et al. Nature Materials 3 (2004).

Fe(001)/MgO(001)/Fe(001)

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 20040

20

40

60

80

100

120

140

160

180

200

Hig

hest

TM

R ra

tio (%

)（at

RT）

Year

MIT

Tohoku IBM

Fujitsu IBMTohoku

INESC Fujitsu

NVEANELVASony

CNRS

CSIC

MPI

AIST

AIST

Al-O barrier

MgO barrier

0

100

200

300

400

500

600

1994 1996 1998 2000 2002 2004 2006 2008Year

TMR

rat

io (%

)

, MgO-barrier MTJs AlO-barrier MTJs

CanonANELVACanonANELVA & AIST& AIST

AISTAIST

IBM

ITIT--programprogramof RR2002of RR2002 AISTAIST

500%@RT(1010%@5K)

AISTAIST

Tohoku Univ.Tohoku Univ.

(Ikeda et al. Tohoku Univ.)

2. TMR in Heusler alloy electrode junction

Annalen der Physik Band 19 (1934) 155-201.

Functions of Heusler Compounds• Magnetic material: Cu2MnAl• Halfmetallic ferromagnet: NiMnSb• Magneto-optical: PtMnSb• Magneto-mechanic: Ni2MnGa• Superconductor: Pd2YSn

Semiconductor: CoTiSb• Heavy fermion: Fe2VAl • Li-conductor: LiMnSb• Magneto-electronic: Co2FeSi• Thermo-electric: TiNiSn• Magneto-caloric: CoMnSb:Nb

19051983

2001

From Prof. Felser

・Spintronics Material : Co2MnSi

Ｘ

7

Tunneling barrier

UHV magnetron sputtering system (P < 1 x 10-7Pa)

Cry

stal

lized

We successfully fabricated highly ordered Co2MnSi

Giant TMR ratio over 1000% at LT is possible in CMS/(Mg/Al/Mg)-O/CMS structure

93%@RT

CoFeB/MgO/CoFeBIkeda et al. JJAP 44 (2005) L1442

Large temperature dependence of TMR ratio should be solved.

To be published in Phys. Rev. Lett.

LSDA : Local Spin Density Appro.

DMFT : Dynamical Mean Field Theory

3. Applications of TMR junction

Application of large TMR junctions

• MRA (Magnetization switching : bit and word lines)• Spin-RAM (Switching by spin transfer torque)• Magnetic reading head of HDD• GPS sensor devices• High frequency oscillator devices•••

electron flow

Ferro1 Ferro2Spacer

Spin-transfer switching (STS) Slonzcewski, JMMM159 (1996)L1

トルク

R

Current

Parallel

Anti-parallel

STS + TMR

Magnetization switching by direct current

G bit + low power MRAMNew devices

field current

Target

precession

0.01

0.1

1

10

Writ

ing

curr

ent (

mA

)

10 100 1000Memory cell size (nm)

Current

Spin transfer switching

CMOS

Issues for Spin-RAM

Current field switching

CMOS maximum IDS

1 mA/1 μm

J = 5

×10

6 A/cm

2

1×10

6 A/cm

2

5×10

5 A/cm

2

Aspect ratio = 2

Gbit Mbit

Switching current : JC0 ~ 5×105 A/cm2

Issues for device application

)cos1(21),( 2 θ

θPPPgtunnel

+=

[ ]2/)2(),(0 Seffext

BS

c MHHPgdeMJ πθμ

αγ+±=±

⎭⎬⎫

⎩⎨⎧−=

00 ln1

ττ p

uB

cc VKTkJJ

Thermal stability

JC0 ~ 5×105 A/cm2

Requirement for devicesJunction Resis. 20 kΩ

Area 80×160 nm2

R・A ~ 200 Ωμm2

Pulse width

τ0 ~ 1 ns

R. H. Koch, PRL92(2004)088302-1

J. C. Slonzcewski, JMMM159 (1996)L1 , PRB71(2005)024411

α : damping constant, Ms : saturation magnetization

d : free layer thickness, P : spin polarization of pinned layer

Switching current density

H

Microwave bridge

h

X-band (9.7 GHz)

TE102 model cavity

Kerr effect

Pump

Probe

Hpulse

Photo-switchHstatic

0 2 4 6Time (ns)

My/

Ms

Line width : ΔHPP

H

Measurement of damping constant α

FMR Pump-probe method

2; ( 2) ; g-2 L/SSG M G gαγ≡ ∝ − ≈

(g-2)2

G(s

ec-1

)

Fe-CoFe-NiCo-Ni

0 0.01 0.02 0.03 0.040

2

4

6

(ｘ 108)

CoFeBCo2Mn(Al,Si)

YIG

Co

Ni

FeCo2MnAl (B2)

Co2MnSi (B2)

Wakitani et al.

Oogane

⊗Co2Fe(Mn)Si (L21)

α=0.004

Summary• TMR ratio more than 100 % (200 %) at room

temperature has been obtained for Heuslerelectrode and Al-O (MgO) barrier tunnel junctions.

• Damping constant α of Heusler alloys (Co2MnSi) is 0.004.

• Rapid decrease of TMR ratio with raising temperature and increasing voltage can be explained by Non-quasiparticle states.

• Heusler alloys are excellent candidate for spintronics materials.

A part of this work was supported by the IT Program of the Research Revolution 2002 (RR2002) by a Grant-in-Aid for Scientific Research from Ministry of Education, Culture, Sports, Science and Technology of Japan and by Strategic Information and Communications R&D Promotion Programme (SCOPE) by Ministry of Internal Affairs and Communicationsand NEDO Spintronics nonvolatile devices project.

ACKNOWLEDGMENTS