Optical spin transfer in GaAs:Mn Joaquin Fernandez-Rossier,

Department of Applied Physics, University of Alicante (SPAIN)

CECAM June 2003, Lyon (FR)

cond-mat/0304492

andA. Núñez , M. Abolfath and A. H. MacDonald

Department of Physics, University of Texas at Austin

•Optical control of magnetization dynamics •Optical injection of electrons and holes in GaAs:Mnwith spin perpendicular to magnetization•Spin transfer in GaAs:Mn

Main Ideas

Current Induced Magnetization

Switching (CIMS)

E.B. Myers et al.,Science 285, 867 (1999).

Current

Magnetization dynamics under electrical spin injection

Co Cu Co

Oiwa et al., PRL 88, 137203 (2001)

Magnetization dynamics under c.w. optical spin injection

GaAs(Ga,Mn)As GaAs

Light Induced Magnetization tilt (LIMT)

Questions•Effect of non-equilibrium quasiparticles on magnetization dynamics?

•SPIN TRANSFER (Slonczewski)

•Spin transfer explains CIMS

•Does spin transfer explain LIMT?

No, low carrier fluency in cw

•Optical Spin transfer with laser pulses?

)( HM

Hdt

d

s

Magnetization Dynamics:

Damping

][E

H

Spin orbit + shape + applied field

Effective field

))((

ntPM s

B

Spin transfer

Quasiparticle spin orientation

Spin Transfer

n

Initiallyn

Recombination orSpin decoherence

The transfer !!

))((

ntPMdt

d

s

B

ST

Photo-carriers/(time volume)

Abolfath, et al. PRB (2001)

Band structure depends on direction of impurity-spin polarization

001

100 110

Anisotropy energy

E [m

eV/n

m3 ]

0.000

0.005

0.010

0.015

001 100 110 001

Effective Field, magnetic anisotropy

][E

H

x=0.055; strain=-0.29%

Time scales:•Electron precession: 0.1 ps•Recombination: 2-20 ps•Electron Spin decoherence: 5-20 ps•Laser pulse duration: 2-20 ps•Ferromagnetic resonance: 60 ps

Optical Spin transfer with laser pulses

Results 1

Energy per pulse: 0.1 mJ/cm2

tL: 3 ps; tR= 2ps, p= n= 1.2 1018 cm3

Weak pumping: ‘FMR’

z

x

z

xz

x

My,Mz

Mx

Energy per pulse: 4.0 mJ/cm2

tL: 3 ps; tR= 2ps, p= n= 5 1019 cm3

z

x

Strong pumping: Switching

z

x

z

x

Spin relaxation time

K K+Q

SPIN WAVE EMISSION

Take Home Message

Optical Spin transfer allows Laser Control of magnetization in

ferromagnetic (III,Mn)-V

E-mail:jfrossier@ua.esWeb: www.ua.es/personal/jfrossier

Coherent vs Incoherent Rotation

ALICANTE

Magnetization dynamics under spin injection

1) Current Induced Magnetization Switching in metals

Electrical Spin injectionCIMS E.B. Myers et

al.,Science 285, 867 (1999).

Oiwa et al., PRL 88, 137203 (2001)GaAs:Mn

2) Light Induced Magnetization tilt in GaAs:Mn

GaAs Optical Spin injectionLIMT