Femtosecond magnetization dynamics in Ni: Spin-orbit induced spin relaxation from first principles

Karel Carva

Charles University, Faculty of Mathematics and Physics, Dept. of Condensed Matter Physics, Praha, Czech Republic

The femtosecond demagnetization discovered in 1996 represents a critical test of magnetization dynamics theories and may lead to many interesting applications. Even now it is still far from being understood on a microscopic level. A number of possible microscopic mechanisms have been proposed. Here we concentrate on the electron-phonon scattering in Ni.

The spin-flip probability associated with electron-phonon scattering in Ni has been estimated - employing the ab initio band structure - to be larger than expected. We calculate the spin-flip Eliashberg function based on ab initio electron-phonon coupling matrix elements, which allows us to obtain the spin-flip probability with much higher accuracy. We extend this method also to the regime of non-equilibrium electron distributions relevant for ultrafast processes. Employing this approach we examine the evolution of the total spin momentum taking into account the real bandstructure of the material. We find that the demagnetization rate is very low for any thermalized electron distributions (including those with electron temperature of the order of thousands Kelvin) compared to the non-thermal distribution present within first femtoseconds following the pump laser.

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