ULTRAFAST NONEQUILIBRIUM SPIN DYNAMICS IN A FERROMAGNETIC THIN-FILM

An ultrafast time-resolved magneto-optical pump probe is applied to st udy spin-relaxation processes in a ferromagnetic CoPt3 alloy film. Fol lowing spin-selective photoexcitation with circularly polarized femtos econd pulses, transient Kerr ellipticity tracks the evolution of the n onequilibrium spin system. We isolate two distinct processes: a subpic osecond component due to the relaxation of coherently spin polarized e lectrons, and a slower component (similar to 10 psec) associated with the evolution of the thermalized spin distribution and the photoinduce d transient magnetization.