Universität Regensburg Dieter Weiss, Universität Regensburg Spin + Electronics = Spintronics Electronic uses electrical charge of electrons…. − − =− ⋅ = ⋅ → 19 31 0 e 1.602 10 C m 9.1 10 kg m* − =± μ = ⋅ 24 B 1 spin 2 9.27 10 J/T ….but electron possesses also spin and hence a magnetic moment, responsible, e.g., for ferromagnetism
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Spin + Electronics = Spintronics · Universität Regensburg Dieter Weiss, Universität Regensburg Spin + Electronics = Spintronics Electronic uses electrical charge of electrons….
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Universität Regensburg
Dieter Weiss, Universität Regensburg
Spin + Electronics = Spintronics
Electronic uses electrical charge of electrons….
−
−
= − ⋅
= ⋅ →
19
310
e 1.602 10 Cm 9.1 10 kg m *
−
= ±
μ = ⋅ 24B
1spin2
9.27 10 J/T
….but electron possesses also spin and hence a magnetic moment, responsible, e.g., for ferromagnetism
Tunneling barrier sandwiched between two ferromagnetic layers
Experiments in TMR geometry
Fe
Fe
GaAs
Universität Regensburg
epitaxialinterface
V
Bias dependence of TMR
J. Moser et al. Appl. Phys. Lett. 89, 162106 (2006)
1 2
1 2
2PPTMR1 PP
=−
Jullière
Universität Regensburg
Outline
Tunneling magneto-resistance
Fe/GaAs/Fe
Spin-orbit interactionin 2DEG
Separation of Rashba-and Dresselhaus
contributions
TAMRTunneling anisotropicmagnetoresistance
Universität Regensburg
Are always two ferromagnetic layers necessary to see a magnetizationdependent resistance?
Our model system: Fe/GaAs/Au with epitaxial Fe/GaAs interface
R1
M
R2
M
1 2R R≠
FeGaAsAu
Spintronic with only one magnetic layer
Fe
GaAs
Au
Universität Regensburg
So far only observed for ferromagneticsemiconductors: (Ga,Mn)As/Al2O3/Au:
Gould et al. PRL 93, 117203 (2004)
TAMR: Tunneling Anisotropic Magnetoresistance
Non-epitaxial interface & amorphous barrier
Universität Regensburg
90°
[110]
[110]
-0,3 -0,2 -0,1 0,0 0,1 0,2 0,3918,0
918,5
919,0
919,5
920,0
920,5
R (Ω
)
B (T)
"TAMR" = -0,2 %
Tunneling magnetoresistance: B along [110] (at +89 mV)-
J. Moser et al., cond-mat/0611406
Universität Regensburg
-0,2 -0,1 0,0 0,1 0,2918,0
918,5
919,0
919,5
920,0
920,5
R (Ω
)
B (T)
"TAMR" = 0,08 %
0°
[110]
[110]
Tunneling magnetoresistance: B along [110] (at +89 mV)
J. Moser et al., cond-mat/0611406
Universität Regensburg
measured at T = 4.2 K and -90 mV
B = 0.5 Tesla
Co/Fe(epi)/GaAs(8nm)/Au
R
M
FeGaAsAu
J. Moser et al., cond-mat/0611406
Angular dependence of TAMR: negative bias
B
Universität Regensburg
measured at T = 4.2 K and +90 mV
B = 0.5 Tesla
Co/Fe(epi)/GaAs(8nm)/Au
J. Moser et al., cond-mat/0611406
Angular dependence of TAMR: positive bias
R
M
FeGaAsAu
T-dependence: see Lobenhofer et al.HL 19.4 Tue 11:30 H14
Universität Regensburg
Fe Au
zl zr
z
EF
φb
0 z BR DH H H H H= + + +
BR x y y x ii l r
i,
1H ( p p ) (z z )=
= σ − σ δ −α∑
z(z)H2
Δ= − ⋅n σ
x x y yD1H ( p (z
z)p )
z∂ ∂⎛ ⎞= σ − σ ⎜ ⎟∂ ∂⎝
γ⎠
2
01H V(z)
2 m(z)⎡ ⎤
= − ∇ ∇ +⎢ ⎥⎣ ⎦
2rl||
1|3 |
,1T (E,keI dEd k [f (E) f (E)])
(2 ) σσ=−
= −π
∑ ∫
particle transmissivity
lα rαγA. Matos-Abiague & J. Fabian cond-mat/0702387
Modelling
Universität Regensburg
lα γ
||w(k ) =y x
x y
k - k- k k 0
α γ⎛ ⎞⎜ ⎟
α + γ⎜ ⎟⎜ ⎟⎝ ⎠
2[110]||
Anisotropy determin ed by
[ ( )] R/R 1 ~ (cos2 1)⋅ → − αγ φ −n w k
Anisotropy vanishes for 0αγ → J. Moser et al., cond-mat/0611406
FeGaAs
Au
n
||w(k )
x
y
z
Origin of anisotropic resistance: SO-interaction duringtunneling (Rashba & Dresselhaus contribution)
Fe Au
zl zr
z
EF
φb
Universität Regensburg
γ = 0
α > γ > 0 α < 0γ > 0
|| ( )ϕkw
( , )x yk kw
α = 0
[100]kx
ky
[100]
kx
ky
ky
[100]
kx
[100]
kx
ky
Universität Regensburg
Anisotropy: Interference of Rashba & Dresselhaus
[100]kx
[110]
[100]
kx
ky[110]
Universität Regensburg
Funding by:
Spin-orbit interaction: Separation of Rashba- and Dresselhauscontributions
Spintronics is interesting both from a fundamental physics point of view as well as from an application perspective. Interplay of newmaterials, new phenomena and new concepts.
Summary
TAMR: Due to interference of Rashba- and Dresselhaus contributionsin epitaxial fm/semiconductor systems.
Many students and colleagues contributed to the work I presented. Many thanks!