Magnetic anisotropy in Fe/U and Ni/U bilayers

TL;DR

This study investigates how magnetic anisotropy varies non-monotonically with uranium layer thickness in Fe/U and Ni/U bilayers, linking quantum well states and electronic structure to observed magnetic behaviors.

Contribution

It provides new insights into the thickness-dependent magnetic anisotropy in U-based bilayers and connects experimental results with electronic structure calculations.

Findings

Non-monotonic magnetic anisotropy dependence on U thickness.

Stronger anisotropy response in Fe/U due to 3d-5f hybridization.

Evidence of perpendicular magnetic anisotropy at larger U thicknesses.

Abstract

Magnetometry measurements of Fe/U and Ni/U bilayer systems reveal a non-monotonic dependence of the magnetic anisotropy for U thicknesses in the range 0 nm - 8 nm, with the Fe/U bilayers showing a more prominent effect as compared to Ni/U. The stronger response for Fe/U is ascribed to the stronger 3d-5f hybridization of Fe and U. This non-monotonic behaviour is thought to arise from quantum well states in the uranium overlayers. Estimating an oscillation period from the non-monotonic data, and comparing it to Density Functional Theory calculations, we find that wavevector matches to the experimental data can be made to regions of high spectral density in (010) and (100) cuts of the electronic structure of{\alpha}-U, consistent with the measured texture in the films. Unexpectedly, there are also indications of perpendicular magnetic anisotropy in a subset of Fe/U samples at relatively large U thickness.