Structure and enhanced magnetization in Fe/Pt multilayers

Abstract

A series of Fe/Pt multilayers, prepared by magnetron sputtering, were characterized by structural [x-ray diffraction (XRD), x-ray-absorption spectroscopy, extended x-ray-absorption fine structure, TEM] and magnetization techniques and extensively investigated by Mössbauer spectroscopy. The Fe layer thickness varied from 3 to 60 Å and that of Pt from 5 to 39 Å. The 3 Å Fe/9 Å Pt sample displays magnetic hyperfine structure at room temperature (RT) while the 3 Fe/19 Pt sample is paramagnetic at RT, demonstrating the effect of the interlayer interaction. Both samples display out of plane magnetic anisotropy with a 39° angle with respect to the normal for the former and 20° for the latter. As the Fe layer thickness increases the magnetic vector turns to the plane. Systematic analysis of the Mössbauer spectra of samples with increasing Fe layer thickness allowed the determination of the magnetic hyperfine field for each Fe monolayer within the Fe layer slab. Hyperfine fields larger than the bulk Fe value appear in all samples with Fe layer thickness larger than 3 Å, and display an oscillatory dependence on the distance of the corresponding Fe monolayer from the interface. These hyperfine field values scale linearly with the average interplanar distance of the Fe layer derived from the refinement of the XRD data for each sample. Fe atomic magnetic moments determined from superconducting quantum interference device magnetometry and Rutherford backscattering spectroscopy measurements are also larger than the bulk Fe value, approaching it for large Fe layer thickness. The parameters determining the enhancement of magnetization in the Fe/Pt system are discussed. © 1996 The American Physical Society.