Size-dependent magnetic spin and orbital moments of Fe nanoparticles deposited onto Co/W(110)

In situ x-ray magnetic circular dichroism (XMCD) measurements by means of total electron-yield detection have been carried out on mass-filtered Fe nanoparticles with diameters ranging from 6 to 10 nm upon deposition onto Co/W(110). The shape as well as the crystallographic structure has independently been investigated by means of high-resolution transmission electron microscopy. An evaluation of the XMCD spectra revealed bulklike magnetic spin moments but strongly enhanced magnetic orbital moments after correcting for electron-yield saturation effects. The observed size dependence of the magnetic moments cannot be understood in simple core shell models where the core is assumed to be bulklike and only the outer shell possesses enhanced values according to their reduced coordination at the surface. Instead, size-dependent distortions of the crystal lattice due to surface and interfacial tension as well as mesoscopic relaxations at the surface facets of the nanoparticles are considered as the origin of the observed large orbital moments.