Evidence of electron-phonon mediated spin flip as driving mechanism for ultrafast magnetization dynamics in 3d ferromagnets

Despite intense experimental effort, theoretical proposals, and modeling approaches, a lack of consensus exists about the intrinsic mechanisms driving ultrafast magnetization dynamics in 3d ferromagnets. In this Letter, we find evidence of an electron-phonon mediated spin flip as the driving mechanism for the ultrafast magnetization dynamics in all three 3d ferromagnets: nickel, iron, and cobalt. We use a microscopic three-temperature model with parameters calculated from first principles, which has been validated by a direct comparison to the electron and lattice dynamics extracted from previous experiments. By a direct comparison to the experimentally mea-sured magnetization dynamics for different laser fluences, we determine the spin-flip probability of each material. We find robust evidence that relatively small values of the spin-flip probability enable ultrafast demagnetization in all three 3d ferromagnets.