Ferromagnetic model system with spin-orbit coupling: Dynamical gap and effective spin-flip scattering

We investigate ultrafast magnetization dynamics due to electron-phonon interaction in a ferromagnetic Rashba model, which includes spin-orbit coupling and a Stoner mean-field splitting. By computing the reduced spin-density matrix including explicitly spin-independent electron-phonon scattering at the level of Boltzmann-type scattering integrals, we investigate the influence of a time-dependent Stoner mean field on the magnetization dynamics. We find that the dynamical gap increases the magnetization quenching on short timescales and slows down the remagnetization process. We further show how the noncollinear dynamics of electronic spins in the band structure with internal spin orbit fields can be approximated by effective spin-flip scattering matrix elements.