Non-thermal excitation and control of magnetization in Fe/GaAs film by ultrafast laser pulses

We present our recent study of non-thermal excitation and coherent control of spin reorientation in 10-nm epitaxially grown Fe thin films by low-energy femtosecond laser pulses. The magnetization dynamics and hysteresis curves were recorded by pump-probe differential magnetic Kerr (DMK) spectroscopy using linearly polarized laser beams. A sharp switching in DMK signal is observed when we rotated the pump polarization. This result indicates a non-thermal origin of magnetization excitation and reorientation in Fe films. We reveal that spins can interact coherently with the polarization induced by the pulsed laser field in magnetic metals. Such opto-magnetic interactions are instantaneous and are only limited in time by the properties of laser pulses. Our results suggest the feasibility of ultrafast optical control of both the magnetization and the demagnetization responses in magnetic films. (C) 2012 American Institute of Physics. [doi:10.1063/1.3675158]