Intrinsic and nonlocal Gilbert damping parameter in all optical pump-probe experiments

The study of magnetization dynamics on the femtosecond time scale is an important task for the implementation of future ultrafast spintronics. With the time resolution inherent using femtosecond laser pulses in all optical pump-probe experiments, the basic time constants of magnetic precessional modes as well as the energy dissipation processes, which determine the Gilbert damping, can be studied. The dominant magnetic relaxation modes for the thin Ni films have frequencies in the range of 1.5-13 GHz. The corresponding Gilbert damping parameter is found to be dependent on the precession mode. The alpha values range from 0.05 to 0.8 for highly damped modes. The nonlocal Gilbert damping due to evanescent spin currents and two-magnon scattering is studied for double layers Ni/Cr/Si(100) with varied Ni thicknesses. A large increase of the damping parameter for films with a thinner Ni layer is observed. (C) 2006 American Institute of Physics.