Evolution from ultrafast demagnetization to magnetization reversal at the Fe sites in Gd23Fe67Co10 with laser fluence, observed by the element-selective magneto-optical Kerr effect using an X-ray free electron laser

Abstract In the present study, we investigated the magnetization dynamics of a Gd 23 Fe 67 Co 10 nanofilm. We subjected the nanofilm to a time-resolved experiment to examine its magneto-optical effect using an X-ray free electron laser. By tuning the energy of the photons to the core-level resonance of the Fe absorption edge, we selectively determined the magnetic behavior of the elements at the Fe site in the nanofilm. When triggered by an ultrashort pulse of infrared radiation, the materials underwent demagnetization and magnetic reversal, depending on fluence of the laser. The following relaxation process was found to be associated not only with the fast recursion but also with a long sustention of the reversed magnetization. The experimental observation consistently match with the recent prediction by the magnetic dynamic simulation. The ultrafast dynamics was triggered by the ultrafast thermal effect and it was recovered toward the initial state in the non-thermal manner.