Microscopic model for femtosecond magnetization dynamics

We present a microscopic model that explains quenching of the magnetization of ferromagnetic transition metals such as nickel within a picosecond after laser excitation. Our model 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 the Weiss model. An Elliot-Yafet type of spin-flip probability αEY is included for each electron-phonon (e-p) scattering event. We show that even though the demagnetization in our model is mediated by phonon scattering, it is possible to obtain a demagnetization time that is shorter than the e-p equilibration (and even thermalization) time.