Magnetism of exposed and Co-capped Fe nanoparticles

The effect of capping a dilute assembly of nanoscale mass-selected Fe clust ers with a Co thin film has been studied using X-ray magnetic circular dich roism (XMCD). The clusters, containing around 400 atoms, were deposited in situ from a gas-aggregation source onto highly oriented pyrolytic graphite. The exposed clusters possess magnetic moments that are enhanced compared t o the bulk, by around 4% for m(spin) and around 75% for m(orb). In addition , a surface core level shifted component is observed in the L-3.2 XMCD spec trum. Upon adding the Co layer, the surface component disappears, m(orb) is decreased for the Fe clusters, and m(spin) increases. The exposed clusters are magnetically isotropic but a strong in-plans anisotropy is observed af ter depositing the Co overlayer. We attribute this to the shape of the Co i slands in which the Fe clusters are embedded. (C) 2000 Elsevier Science B.V . All rights reserved.