Permanent-magnet properties of thermally processed FePt and FePt-Fe multilayer films

FePt single-layer and FePt-Fe multilayer thin films are prepared by magnetron sputtering. By varying the Pt content, FePt, Fe₃Pt, or a mixture of FePt and Fe₃Pt can be obtained in Fe-Pt single layers. In annealed FePt-Fe multilayers, the coercivities decrease with the introduction of Fe layers compared to FePt single layers, while the magnetization increases. The single-phase behavior of the hysteresis loops of FePt-Fe multilayers indicates the existence of exchange coupling in these materials. For one FePt-Fe sample with optimized exchange coupling, the intrinsic properties correspond to an energy product of 19 MGOe. The texture of the magnets is determined by the [111] orientation of the crystallites. This means that the easy magnetization directions of the FePt grains form an angle of 54.7° with the film normal, but are randomly oriented in the film plane. It is analyzed how this easy-axis distribution affects the magnetic hysteresis.