Influence of interface effects on a rare-earth crystal field in iron–rare-earth multilayers

M\"ossbauer spectroscopy and magnetization measurements (mean and high field) were carried out on Fe-R multilayers, where R=Nd and Tm. From the high-field (20-T) magnetization measurements, the magnetic moment of 3.27 μB/at. for neodymium was found. It is the first experimental evidence of the free-ion magnetic moment for Nd metal in multilayers. Perpendicular and in-plane anisotropy directions for NdFe and TmFe multilayers, respectively, were observed. An original explanation of these phenomena, taking into account modifications of the rare-earth crystal field due to the layered structure and artificial periodicity, is proposed.