ORBITAL MAGNETIC MOMENTS OF CO IN MULTILAYERS WITH PERPENDICULAR MAGNETIC ANISOTROPY

The out-of-plane orbital magnetic moment of Co in Co/[ital X] multilayers ([ital X]=Pd, Pt, and Ni) with perpendicular magnetic anisotropy has been investigated using x-ray magnetic-circular-dichroism spectroscopy. The orbital [ital d] moment per Co atom, [ital m][sub orb][sup [perpendicular]], is considerably enhanced by (0.15[plus minus]0.02)[mu][sub [ital B]] and (0.07[plus minus]0.02)[mu][sub [ital 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 [ital not] scale with the spin-orbit coupling parameter [xi][sub SO] of Ni-3[ital d], Pd-4[ital d], and Pt-5[ital d] bands despite strong [ital d]-[ital 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 [ital m][sub orb][sup [perpendicular]] with the intrinsic uniaxial anisotropy constant [ital K][sub [ital u],1][sup Co] per Co volume is observed. This experimental finding is interpreted in conjunction with recent [ital ab] [ital 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.