recent progress in large tunnel … progress in large tunnel magnetoresistance junctions 1. a little...
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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
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1. A little review of MTJs
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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
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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).
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-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)
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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
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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.)
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2. TMR in Heusler alloy electrode junction
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Annalen der Physik Band 19 (1934) 155-201.
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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
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X
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7
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Tunneling barrier
UHV magnetron sputtering system (P < 1 x 10-7Pa)
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Cry
stal
lized
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We successfully fabricated highly ordered Co2MnSi
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Giant TMR ratio over 1000% at LT is possible in CMS/(Mg/Al/Mg)-O/CMS structure
93%@RT
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CoFeB/MgO/CoFeBIkeda et al. JJAP 44 (2005) L1442
Large temperature dependence of TMR ratio should be solved.
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To be published in Phys. Rev. Lett.
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LSDA : Local Spin Density Appro.
DMFT : Dynamical Mean Field Theory
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3. Applications of TMR junction
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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•••
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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
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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
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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
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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
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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
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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.
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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