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

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

bulk~100nm - 1m wide bars

Sensitivity of AMR to lattice distortions

GaAs

GaMnAs

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