Ultrafast optical control of coercivity in GaMnAs

Femtosecond optical control of the magnetization and coercive field is demonstrated in GaMnAs using time-resolved magneto-optical Kerr effect techniques. These experiments reveal a near-complete, subpicosecond collapse of the hysteresis loop, consistent with femtosecond demagnetization. On longer time scales (similar to 300 ps) an increase in coercivity is observed, attributed to hole-mediated enhancement of the domain wall energy. (C) 2008 American Institute of Physics.