Magnetic polarization of copper in Cu-capped Co clusters

Magnetic anisotropy of Co nanoparticles homogeneously dispersed in alumina is increased by capping the particles with copper. In the present work, we investigate this effect by measuring X-ray magnetic circular dichroism (XMCD) at the K and L2,3 edges of Co and Cu atoms. We demonstrate that orbital-to-spin ratio at the Co 3d states is increased by capping with Cu, explaining the observed enhancement of the macroscopic anisotropy. Hybridization between Co and Cu at the interface produces an electronic transfer between them. Clear induced magnetic moments are observed in copper, both in the 4p states and in the 3d states.