Spin-orbit coupling and spintronics in ferromagnetic semiconductors (and metals) Tomas Jungwirth...
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Transcript of Spin-orbit coupling and spintronics in ferromagnetic semiconductors (and metals) Tomas Jungwirth...
Spin-orbit coupling and spintronics in ferromagnetic Spin-orbit coupling and spintronics in ferromagnetic semiconductors (and metals)semiconductors (and metals)
Tomas Jungwirth
University of Nottingham Bryan Gallagher, Tom Foxon,
Richard Campion, Kevin Edmonds, Andrew Rushforth, Chris King et al.
Hitachi Labs., UK & JapanJorg Wunderlich, Byong-Guk Park,
Andrew Irvine, Elisa De Ranieri, Samuel Owen, David Williams, Akira, Sugawara, et al.
Institute of Physics ASCR Alexander Shick, Jan Mašek, Josef Kudrnovský,
František Máca, Karel Výborný, Jan Zemen, Vít Novák, Kamil Olejník, Jairo Sinova et al.
Outline
1. Intro – spin-orbit coupling in spintronics
2. GaMnAs based spintronic devices
3. GaMnAs and other spin-orbit coupled ferromagnetic materials
SO-couping = E&M and postulated electron spin
nucleus rest frameelectron rest frame
Lorentz transformation Thomas precession
lSEvSS
dr
rdV
ermc
e
mc
egH B
SO
)(1B
22
2 2
ee--… it’s all about spin and charge of electron communicating
vI Q rE3
04 r
Q
3
0
4 r
rIB
EvEvB 200
1
c& &
Spintronics
Spin-orbit couping
2
Ferromagnetism = Pauli exclusion principle & Coulomb repulsion
total wf antisymmetric = orbital wf antisymmetric * spin wf symmetric (aligned)
DOS
DOS
ee--
ee--
ee--
… collectivecommunication
macroscopic moment large effects
AMRAMR~ 1% MR effect~ 1% MR effect
GMRGMR~ 10% MR effect~ 10% MR effect
<
FM only ( )
TMRTMR~ 100% MR effect~ 100% MR effect
TDOS TDOS
FM & SO-coupling (M )
+ linear sensing, low-noise - low MR, low-resistance
+ larger MR
- low-resistance, non-linear, spin-coherence, exchange biasing or interlayer coupling, higher noise
+ very large MR, high resistance, bistable memory
- non-linear, spin-coherence, exchange biasing, higher noise
AuAlOxAu
TAMRTAMR CBAMRCBAMR
TDOS (M ) chem. pot.
Combining “+” and eliminating “-” of AMR and TMR(GMR) & SET gating spintronic transistor
SO-coupling magnetocrystalline anisotropies sensitivity to lattice distortions
Ferromagnetic/magnetostrictive
Ferroelectric/piezoelectric Semicondicting/gatable
magneto-sensors, transducors, memory, storage
electro-sensors, transducors, memory
transistors, processorsFeFET
piezo/FMhybrids FM semiconductors
Systems integrating all three basic elements of current microelectronics
Outline
1. Intro – spin-orbit coupling in spintronics
2. GaMnAs based spintronic devices
3. GaMnAs and other spin-orbit coupled ferromagnetic materials
(Ga,Mn)As: archetypical system for SO-coupling based spintronics research
Mn-d-like localmoments
As-p-like holes
Mn
Ga
AsMn
SW-transf. Jpd SMn . shole
Dilute Mn-doped SC: sensitive to doping; 100smaller Ms than in conventional metal FMs weak dipolar fields
Mn-Mn coupling mediated by holes in SO-coupled SC valence bands:sensitive to gating, comparable magnetocrystalline anisotropy energy and stiffness to metal FMs
Model sp-d ferromagnet:kinetic-exchange (Jpd) & host SC bands provides simple yet often semiquantitative description
GMMGG0
20
C
C
e
)M(V&)]M(VV[CQ&
C2
)QQ(U
electric && magneticmagnetic
control of Coulomb blockade oscillations
Coulomb blockade AMR – anisotropic chemical potential
Q
0
'D
'
e
)M(Q)Q(VdQU
Source Drain
GateVG
VDQ
[010]
M[110]
[100]
[110][010]
M || <110> M || <100>
(M)
Tunneling AMR – anisotropic TDOS
TAMR in GaMnAs
GaMnAsAuAlOx Au
Res
ista
nce
Magnetisation in plane
M perp.
M in-plane
~ 1-10% in metallic GaMnAs
Huge when approaching MIT in GaMnAs
Anisotropc tunneling amplitudes
One
One
0.1-1 m
(b)
Strain controlled micromagnetics
… plus 100-10x smaller currents for DW switching and 100-10x weaker dipolar crosslinks prospect for dense integration of magnetic microelements switchable by low currents
500 nm
DW structure and dynamics directly reflecting e.g. (strain dependent) competition between uniaxial and cubic anisotropies
strain ~ 10-4
Outline
1. Intro – spin-orbit coupling in spintronics
2. GaMnAs based spintronic devices
3. GaMnAs and other spin-orbit coupled ferromagnetic materials
Magnetism in systems with coupled dilute moments and delocalized band electrons
(Ga,Mn)As
cou
pli
ng
str
eng
th /
Fer
mi
ener
gy
band-electron density / local-moment density
VB-CB
VB-IB
Mn-acceptor level (IB)
Short-range ~ M . s potential
- additional Mn-hole binding - ferromagnetism - scattering
GaAs:Mn extrinsic semiconductorGaAs VB
GaMnAs disordered VB
2.2x1020 cm-3
MIT in GaAs:Mn at order of magnitude higher doping than quoted in text books
MIT (and ferromagnetism) at relatively large doping suppressed gating effect
MIT in p-type GaAs:- shallow acc. (30meV) ~ 1018 cm-3
- Mn (110meV) ~1020 cm-3
d4
d
Weak hybrid.Delocalized holeslong-range coupl.
Strong hybrid.Impurity-band holesshort-range coupl.
d 5 d 4 no holes
InSb, InAs
GaN
AlAs
d5
Search for optimal III-V host
optimal combination of large SO-cupling, hole delocalization, hole-Mn coupling
SO
-co
up
lin
g s
tren
gth
, b
and
-par
abo
lici
ty
GaP
GaAs
I(II,Mn)V dilute-moment ferromgantic semiconductors
III = I + II Ga = Li + Zn
• GaAs and LiZnAs are twin semiconductors
• Prediction that Mn-doped are also twin ferromagnetic semiconductors
• No limit for Mn-Zn (II-II) substitution within the same crystal structure
• Independent carrier (holes and electrons) doping by Li-Zn stoichiometry adjustment
+ interstitial
Rock Salt
FCC
Zinc Blende – (III,Mn)V
+ interstitial+ interstitial
+ interstitial
+ interstitial
I(II,Mn)V
Half Heusler (NiMnSb)
I(II,Mn)V as a link between DMSs and high-Tc half-metalic Heuslers,all comaptible with III-V technology
High Tc large SO-coupling TM thin films and ordered alloys
FM TMheavy TM
spontaneous moment
mag
net
ic s
usc
epti
bil
ity sp
in-o
rbit co
up
ling
FM TMheavy TM
heavy TM
FM TM
Key: large induced moment on strongly SO-coupled heavy TM
B. G. Park, J. Wunderlich, D. A. Williams, S. J. Joo, K. Y. Jung, K. H. Shin, K. Olejnik, A. B. Shick, and T. Jungwirth: Tunneling anisotropic magnetoresistance in multilayer-(Co/Pt)/AlOx/Pt structures, submitted to Phys. Rev. Lett. (2007)
Akira Sugawara, H. Kasai, A. Tonomura, P. D. Brown, R. P. Campion, K. W. Edmonds, B. L. Gallagher, J. Zemen, and T. Jungwirth: Domain walls in (Ga,Mn)As diluted magnetic semiconductor, Phys. Rev. Lett. in press (2007)
A. W. Rushforth, K. Výborný, C. S. King, K. W. Edmonds, R. P. Campion, C. T. Foxon, J. Wunderlich, A. C. Irvine, P. Vašek, V. Novák, K. Olejník, Jairo Sinova, T. Jungwirth, B. L. Gallagher: Anisotropic magnetoresistance components in (Ga,Mn)As, Phys. Rev. Lett. 99 (2007) 147207
J. Masek, J.Kudrnovsky, F. Maca, B. L. Gallagher, R. P. Campion, D. H. Gregory, and T. Jungwirth: Dilute moment n-type ferromagnetic semiconductor Li(Zn,Mn)As, Phys. Rev. Lett. 98 (2007) 067202
J. Wunderlich, T. Jungwirth, B. Kaestner, A. C. Irvine, K.Y. Wang, N. Stone, U. Rana, A. D. Giddings, A. B. Shick, C. T. Foxon, R. P. Campion, D. A. Williams, B. L Gallagher: Coulomb Blockade Anisotropic Magnetoresistance Effect in a (Ga,Mn)As Single-Electron Transistor, Phys. Rev. Lett. 97 (2006) 077201
T. Jungwirth, Jairo Sinova, J. Mašek, J. Kučera, and A.H. MacDonald: Theory of ferromagnetic (III,Mn)V semiconductors, Rev. Mod. Phys. 78 (2006) 809
C. Rüster, C. Gould, T. Jungwirth, J. Sinova, G.M. Schott, R. Giraud, K. Brunner, G. Schmidt, L.W. Molenkamp: Very Large Tunneling Anisotropic Magnetoresistance of a (Ga,Mn)As/GaAs/(Ga,Mn)As Stack, Phys. Rev. Lett. (2005) 027203