Spin Dynamics in Rare Earth Doped Cobalt Ferromagnetic Films

We have investigated the demagnetization (τM) and the precession damping (η) times of the magnetization of Co ferromagnetic films doped with rare earth elements excited by femtosecond laser pulses. Both times are measured as a function of the absorbed laser energy density E0 and doping concentration cRE with rare-earth elements. The results indicate a priori no direct connection between τM and η with respect to spin-impurity scattering processes, while both times depend on E0, due to a raise of respectively the electronic and lattice temperatures.