Femtosecond dynamics of the spin population in metallic ferromagnets

Summary form only given. Recent experiments have revealed an ultrafast optically-induced dynamics in the time-resolved linear magneto-optical (MO) signals obtained in metallic ferromagnetic samples. An important question raised by these experiments is to know how much of the observed dynamics is due to the excited electronic populations or to their spins. In this paper we report on the study of a thin film of CoPt/sub 3/ alloy with a temporal resolution that allowed us to clearly resolve for the first time the ultrafast characteristic time of the MO signal. Moreover, by carefully separating the time evolution of the diagonal and nondiagonal elements of the dielectric tensor, we show that during the thermalization process of the electronic population, the spin population is modified. This allows us to clarify the respective role of charges and spins on the femtosecond time scale.