1. Theory of Optically Induced Magnetization Switching in GaAs:Mn J. Fernandez-Rossier, A. Núñez, M. Abolfath and A. H. MacDonald Department of Physics, University of Texas at Austin March Meeting 2003, Austin (TX) Optical injection of electrons and holes in GaAs:Mn with spin perpendicular to magnetization Spin transfer in GaAs:Mn Optical analog of current induced switching in ferromagnetic metals

2. Time scales: Electron precession: 0.1 ps Recombination: 2 ps Electron Spin decoherence: 5-20 ps Laser pulse duration: 10-20 ps Ferromagnetic resonance: 60 ps

3. Magnetization Dynamics: Damping ST Spin orbit + shape + applied field Spin transfer Light propagation axis Effective field

4. Spin Transfer Initially At Recombination The transfer !! Photo-carriers/(time volume)

5. Abolfath, et al. PRB (2001) Band structure depends on direction of impurity- spin polarization 001 100 110 Anisotropy energy E [meV/nm 3 ] 0.000 0.005 0.010 0.015 001 100 110 001 Effective Field, magnetic anisotropy x=0.055; strain=-0.29%

6. Results 1

7. Results 2

8. Conclusions Spin torque: no current needed Laser Control of magnetization orientation in GaAs:Mn Email: joaquin@physics.utexas.edu