In-plane orbital moment anisotropy in fcc Fe0.65Ni0.35 ultrathin films grown on stepped Cu(1 1 1) surfaces

Fe0.65Ni0.35 ultrathin films 3.5 monolayer thick have been grown on a vicinal Cu(1 1 1) surface in order to correlate the in-plane step-induced magnetic anisotropy deduced from X-ray magnetic circular dichroism (XMCD) to the crystal structure and morphology of the films obtained by scanning tunneling microscopy and surface extended X-ray absorption spectroscopy. Magnetic moments are derived by applying the well-known sum rules to XMCD data and their anisotropies are determined by measurements obtained through various geometric conditions implying different polar and azimuth angles. The results for 3.5 ML alloy films show that the orbital moment ML depends strongly on the azimuth angles while the effective spin moment MeffS is found nearly isotropic. We explain the strong in-plane orbital moment anisotropy in the light of the structural in-plane strains induced by the steps, the growth mode and the lattice parameter relaxation in this thickness range.