Magnetic polarization of noble metals by Co nanoparticles in M-capped granular multilayers (M = Cu, Ag, and An):: An x-ray magnetic circular dichroism study

X-ray magnetic circular dichroism spectra have been recorded at the L(2,3) edges of Co, Cu, Ag, and Au, and at the K edges of Co and Cu for a series of multilayer systems of partially self-assembled Co nanoparticles, both capped with alumina and with different metals (Cu, Ag, and Au). The orbital and spin moments M(L) and m(S) and their ratio M(L)/M(S), for Co, Cu, Ag, and Au, have been determined from those measurements. The trend of increasing M(L)/M(S) for Co is the same as found for increasing the effective anisotropy K(eff) alumina < Cu < Ag < Au capped. It is shown that the relative increase in the surface contribution for both quantities, (M(L)/m(S))(surf) and K(S), is directly correlated. It is argued that the increase in M(L) with metal capping actually reflects an increase in the anisotropy of the orbital moment for the Co surface atoms. The redistribution of the number of holes in the noble metal bands by hybridization with the Co surface atom 3d band and the polarization of the nd band by exchange interaction with the Co bands give rise to the magnetic moments derived for the three noble metals investigated.