Microscopic model for fs magnetization dynamics

Over the past few years a wealth of new data on laser-induced ultrafast magnetization dynamics has become available. By now, it is generally agreed on that within a few hundred femtoseconds after laser excitation of ferromagnetic transition metals such as nickel the spin system equilibrates at a reduced magnetization. As to the underlying physics that enables such an ultrafast response little is known. In this presentation we report first results of a fully microscopic approach based on a simple model Hamiltonian that describes the interactions between a Fermi sea of (spinless) electrons, an ensemble of two level oscillators representing the phonon system, and a magnetic degree of freedom described by a Weiss model. In particular we include an Elliot-Yafet type of spin-orbit induced spin scattering by assigning a spin- flip probability aEY to each electron-phonon (e-p) scattering event. The e-