In-plane orbital moment anisotropy in fcc Fe0.65Ni0.35 ultrathin films grown on stepped Cu(111) surfaces

Fe0.65Ni0.35 ultrathin films 3.5 monolayer thick have been grown on a vicin al Cu(1 1 1) surface in order to correlate the in-plane step-induced magnet ic anisotropy deduced from X-ray magnetic circular dichroism (XMCD) to the crystal structure and morphology of the films obtained by scanning tunnelin g microscopy and surface extended X-ray absorption spectroscopy. Magnetic m oments are derived by applying the well-known sum rules to XMCD data and th eir anisotropies are determined by measurements obtained through various ge ometric conditions implying different polar and azimuth angles. The results for 3.5 ML alloy films show that the orbital moment M-L depends strongly o n the azimuth angles while the effective spin moment M-S(eff) is found near ly isotropic. We explain the strong in-plane orbital moment anisotropy in t he light of the structural in-plane strains induced by the steps, the growt h mode and the lattice parameter relaxation in this thickness range. (C) 20 01 Elsevier Science B.V. All rights reserved.