In-plane magnetocrystalline anisotropy observed on Fe/Cu(111) nanostructures grown on stepped surfaces

Abstract

Magnetic in-plane and out-of-plane anisotropies measured by angle dependent x-ray magnetic circular dichroism (XMCD) on fcc Fe nanostructures are discussed and compared with fcc FeNi nanostructures. All studies were performed using XMCD at the Fe ${L}_{2,3}$ edges for Fe grown on a Cu(111) vicinal vic surface. The step induced in-plane anisotropy in the step decoration regime is analyzed by measuring the orbital magnetic moment dependence as a function of the in-plane azimuth and out-of-plane incidence angles. In the one-dimensional limit where the out-of-plane magnetic easy axis dominates, Fe/Cu(111) shows a large in-plane orbital magnetic moment anisotropy leading to a magnetocrystalline anisotropy energy of 0.4 meV/atom and an in-plane magnetic easy axis perpendicular to the steps. In the nanometer scale the aspect ratio of the elongated rectangular Fe stripes are found to be responsible for the in-plane and out-of-plane anisotropy. This is coherent with previous findings where the circular shaped fcc ${\mathrm{Fe}}_{0.65}{\mathrm{Ni}}_{0.35}$ nanostructures do not show any in-plane anisotropy. The three-dimensional nanostructures are characterized by magnetic orbital moments connected with the number of broken bonds in the direction of the quantization axis defined by the direction of the saturation field. The microscopic origin of the in-plane large orbital magnetic moment anisotropy is attributed to the nanometer size of the structures perpendicular to the steps and to the asymmetry of the number of broken bonds in the plane.