Part 3

Report
Spintronics: How spin can act on charge carriers and vice versa
Tomas Jungwirth
Institute of Physics Prague
University of Nottingham
Mott without spin current
Mott with spin current
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
Spintronics
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From Wikipedia, the free encyclopedia
Spintronics (a pormanteau meaning
spin transport electronics)....
GMR
1988
MRAM
2006
Dirac without current through magnet
Dirac with current through magnet
I
AMR
1857
I
HD Read-heads
1990‘s
Mott with antiferromagnets
Mott with ferromagnets
I
I
I
Dirac with ferromagnets
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
I
Dirac with antiferromagnets
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I
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Magnetic-field control of FMs:
scales with current
Control by current
via spin torques:
scales with current
density
Control by photo-carriers
via spin torques:
sub ps timescales
0.1 pJ
Relativistic spin-orbit torques
might work equally well in
AFMs plus photocarriers in SCs
Electro-static field control via relativistic
magnetic anisotropy effects:
1fJ
Should work equally well or better
in AFMs: more choices including SCs
(or piezo-electric)
Writing by current
via spin torques:
scales with current
density
Writing by photo-carriers
via spin torques:
sub ps timescales
0.1 pJ
Relativistic spin-orbit torques
might work equally well in
AFMs plus photocarriers in SCs
Optical spin-transfer torque
OSTT
Pn
s
M
M
s
Pn
M
M


Němec, Tesařová, Novák, TJ et al. Nature Phys.’12, Nature Photonics ‘13, Nature Commun. ‘13
Fernandez-Rossier, Nunez, Abofath, MacDonald cont-mat/0304492
Optical spin-transfer torque
OSTT
Pn
s
s
Pn
M
M

Němec, Tesařová, Novák, TJ et al. Nature Phys.’12, Nature Photonics ‘13, Nature Commun. ‘13
Fernandez-Rossier, Nunez, Abofath, MacDonald cont-mat/0304492
Optical spin-transfer torque
OSTT
Pn
s
s
Pn
M
M

Němec, Tesařová, Novák, TJ et al. Nature Phys.’12, Nature Photonics ‘13, Nature Commun. ‘13
Fernandez-Rossier, Nunez, Abofath, MacDonald cont-mat/0304492
Electrical spin-transfer torque
Antidamping-like (adiabatic) STT
OSTT
Pn
s
M
Zhang and Li PRL 2004
Vanhaverbeke et al. PRB 2007,......
Electrical spin-transfer torque
Field-like (non-adiabatic) STT
s
Pn
M
Zhang and Li PRL 2004
Vanhaverbeke et al. PRB 2007,......
Electrical spin-transfer torque
Antidamping-like STT
Field-like STT
~
1
1  ( ex /  s ) 2
 ex /  s
1  ( ex /  s ) 2
STTNA / STTAD     ex /  s
small  in weakly SO-coupled dense-moment metal FMs
large  in strongly SO-coupled dilute-moment (Ga,Mn)As
Electrical spin-transfer torque: current induced DW motion
Electrical spin-transfer torque: current induced DW motion
vDW
=0
“intrinsic” pinning
j
jC

Antidamping STT
Antidamping-like STT
Zhang & Li, PRL 93, 127204 (2004)
Vanhaverbeke & Viret, PRB 75, 024411 (2007)
Electrical spin-transfer torque: current induced DW motion
vDW
<
j
jC

Antidamping STT
Antidamping-like STT
Field-like STT
Zhang & Li, PRL 93, 127204 (2004)
Vanhaverbeke & Viret, PRB 75, 024411 (2007)
Electrical spin-transfer torque: current induced DW motion
vDW
>
<
j
jC
jC

Antidamping STT
Antidamping-like STT
Field-like STT
Zhang & Li, PRL 93, 127204 (2004)
Vanhaverbeke & Viret, PRB 75, 024411 (2007)
Steady-state carrier spin polarization

s

 torque dM
dt
QM averaging in non-equilibrium
Electrical spin injection
Non-relativistic STT

Pn
Steady state
Optical spin injection
External
antidamping-like torque

Pn
M
Steady-state carrier spin polarization

s

 torque dM
dt
QM averaging in non-equilibrium
Electrical spin injection
Relativistic SOT
Internal
Steady state
Optical spin injection
M

s
Steady-state carrier spin polarization

 torque dM
dt
Linear response: eigenstates of H
& non-equilibrium distribution
Electrical drift and relaxation:
broken inversion symmetry
Relativistic SOT

s
Internal
Steady state

s

M
Optical generation and relaxation

s

s
Paramagnets
Spin-orbit
Magnetic field of moving nucleus
in electron‘s rest frame
Spin-galvanic effect
= SOT without

s
acting on

M
Electrical drift and relaxation:
broken inversion symmetry

s
Aronov, Lyanda-Geller, JETP ’89, Edelstein SSC ’90, Ganichev et al. Nature ‘02
Paramagnets
Spin-orbit
Magnetic field of moving nucleus
in electron‘s rest frame
Spin Hall effect
MRAM switching by in-plane current  SHE spin-current  non-relativistic STT
Ralph, Buhrman,et al., Science ‘12
Hall antidamping STT
SHE in Pt acts as the external polarizer
MRAM switching by in-plane current  attractive alternative to perp. current STT
Conventional perpendicular current STT
MRAM switching by in-plane current  attractive alternative to perp. current STT
Conventional perpendicular current STT
Competing scenario: In-plane current swithing by relativitic SOT due to broken
structural inversion symmetry at Co/Pt?
Miron et al., Nature ‘11
Ralph, Buhrman et al.: SHE
Miron et al.: SOT
-We see antidamping-like torque
-We also see antidamping-like torque
-SOT is field-like so we exclude it
-SOT is field-like but maybe there is some
antidamping-like SOT as well
- non-relativistic STT in metals is
dominated by the antidamping torque
Where could a comparable strength antidamping-like SOT come from?

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