Comprehensive view on ultrafast dynamics of ferromagnetic films



The relaxation mechanisms in magnetic thin films studied in all-optical pump probe experiments involve electrons, spin and lattice as well as the different couplings in between those. With this technique, the evolution of the electron and spin dynamics can be studied directly in real time from 100 fs to ns timescale. We give a comprehensive view of the current understanding of the processes involved. The details of the spin relaxation-mechanisms on the ultrafast and Landau-Lifshitz-Gilbert time scales are still unknown. Time-resolved reflectivity measurements on ferromagnetic transition metal films give an insight into the specific electronic and lattice relaxation processes. The time-resolved Kerr rotation measurements address the demagnetization and relaxation of the spin system. The demagnetization of the spin system observed in general is strongly coupled to the relaxation mechanism of the electrons, thus follows almost instantaneously the dynamics of the electron system. On the longer time scale, coherent magnetization dynamics is described by the Landau-Lifshitz-Gilbert equation and results in a precession with periods of 50 to 200 ps typical for ferromagnets. The full understanding of the mechanisms will be only accessible by a complete analysis of the interaction between electrons, lattice and spin system. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)