ORBITAL MAGNETIC-MOMENTS OF CO IN MULTILAYERS WITH PERPENDICULAR MAGNETIC-ANISOTROPY

The out-of-plane orbital magnetic moment of Co in Co/X multilayers (X=Pd, Pt and Ni) with perpendicular magnetic anisotropy has been investigated using x-ray magnetic-circular-dichroism spectroscopy. The orbital d moment per Co atom, m(orb)perpendicular-to, is considerably enhanced by (0.15+/-0.02)mu(B) and (0.07+/-0.02)mu(B) in CO/Pd and Co/Pt multilayers, respectively, compared with a single thick Co film. No respective enhancement is found in the case of Co/Ni. This enhancement does not scale with the spin-orbit coupling parameter xi(SO) of Ni-3d, Pd-4d, and Pt-5d bands despite strong d-d mixing which leads to the presence of ferromagnetic moments of Pd and Pt atoms. However, a roughly linear scaling relation of the out-of-plane orbital moment m(orb)perpendicular-to with the intrinsic uniaxial anisotropy constant K(u,1)Co per Co volume is observed. This experimental finding is interpreted in conjunction with recent ab initio and tight-binding band-structure calculations as evidence for a preferential enhancement of the out-of-plane orbital moment of Co in Co/Pd and Co/Pt multilayers.