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 54.7degrees with the film normal, but are randomly oriented in the film plane. It is analyzed how this easy-axis distribution affects the magnetic hysteresis.