Spin-orbit coupling and spintronics in ferromagnetic semiconductors (and metals)

1
Spin-orbit coupling and spintronics in
ferromagnetic semiconductors (and metals)
Tomas Jungwirth
University of Nottingham
Bryan Gallagher, Tom Foxon, Richard
Campion, Kevin Edmonds, Andrew
Rushforth, Chris King 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.
Hitachi Labs., UK Japan Jorg Wunderlich,
Byong-Guk Park, Andrew Irvine, Elisa De Ranieri,
Samuel Owen, David Williams, Akira, Sugawara, et
al.

2

• Outline
• 1. Intro spin-orbit coupling in spintronics
• 2. GaMnAs based spintronic devices
• 3. GaMnAs and other spin-orbit coupled
  ferromagnetic materials

3
Spintronics
its all about spin and charge of electron
communicating
Spin-orbit couping
nucleus rest frame
electron rest frame
Lorentz transformation ? Thomas precession
SO-couping EM and postulated electron spin
2
2
2
4
Ferromagnetism Pauli exclusion principle
Coulomb repulsion
DOS
collective communication
DOS
macroscopic moment ? large effects
5
AMR
GMR
1 MR effect
10 MR effect
FM only (?? ? ??)
FM SO-coupling ?(M )
larger MR - low-resistance, non-linear,
spin-coherence, exchange biasing or interlayer
coupling, higher noise
linear sensing, low-noise - low MR,
low-resistance
TMR
TAMR
CBAMR
100 MR effect
Au
AlOx
Au
TDOS? ? TDOS?
TDOS (M ) chem. pot.
very large MR, high resistance, bistable ?
memory - non-linear, spin-coherence, exchange
biasing, higher noise
Combining and eliminating - of AMR and
TMR(GMR) SET gating ? spintronic transistor
6
SO-coupling ? magnetocrystalline anisotropies ?
sensitivity to lattice distortions
Ferromagnetic/magnetostrictive
magneto-sensors, transducors, memory, storage
piezo/FM hybrids
FM semiconductors
Semicondicting/gatable
Ferroelectric/piezoelectric
electro-sensors, transducors, memory
transistors, processors
FeFET
Systems integrating all three basic elements of
current microelectronics
7

• Outline
• 1. Intro spin-orbit coupling in spintronics
• 2. GaMnAs based spintronic devices
• 3. GaMnAs and other spin-orbit coupled
  ferromagnetic materials

8
(Ga,Mn)As archetypical system for SO-coupling
based spintronics research
As-p-like holes
SW-transf. ? Jpd SMn . shole
Mn-d-like local moments
Dilute Mn-doped SC sensitive to doping
100?smaller 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
9
Coulomb blockade AMR anisotropic chemical
potential
Q
VD
Source
Drain
Gate
VG
magnetic
electric
control of Coulomb blockade oscillations
10
Tunneling AMR anisotropic TDOS
TAMR in GaMnAs
Anisotropc tunneling amplitudes
1-10 in metallic GaMnAs
Huge when approaching MIT in GaMnAs
11
One
Strain controlled micromagnetics
0.1-1 ?m
DW structure and dynamics directly reflecting
e.g. (strain dependent) competition between
uniaxial and cubic anisotropies
500 nm
strain 10-4
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
12
Sensitivity of AMR to lattice distortions
bulk
100nm - 1?m wide bars
GaMnAs
GaAs
13

• Outline
• 1. Intro spin-orbit coupling in spintronics
• 2. GaMnAs based spintronic devices
• 3. GaMnAs and other spin-orbit coupled
  ferromagnetic materials

14
Magnetism in systems with coupled dilute moments
and delocalized band electrons
(Ga,Mn)As
15
GaAs VB
GaAsMn extrinsic semiconductor
Mn-acceptor level (IB)
GaMnAs disordered VB
2.2x1020 cm-3
VB-IB
VB-CB
?
?
Short-range M . s potential - additional
Mn-hole binding - ferromagnetism - scattering
16
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
MIT in GaAsMn at order of magnitude higher
doping than quoted in text books
17
Delocalized holes long-range coupl.
Weak hybrid.
Search for optimal III-V host optimal combination
of large SO-cupling, hole delocalization, hole-Mn
coupling
InSb, InAs
d5
GaAs
GaP
Impurity-band holes short-range coupl.
Strong hybrid.
SO-coupling strength, band-parabolicity
AlAs
d 5 ? d 4
no holes
d
GaN
d4
18
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

19
I(II,Mn)V as a link between DMSs and high-Tc
half-metalic Heuslers, all comaptible with III-V
technology
Zinc Blende (III,Mn)V
I(II,Mn)V
interstitial
FCC
interstitial
interstitial
Half Heusler (NiMnSb)
Rock Salt
interstitial
interstitial
20
High Tc large SO-coupling TM thin films and
ordered alloys
heavy TM
FM TM
FM TM
heavy TM
FM TM
heavy TM
Key large induced moment on strongly SO-coupled
heavy TM
spontaneous moment
spin-orbit coupling
magnetic susceptibility
21
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. Kucera,
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