Magnetism of exposed and Co-capped Fe nanoparticles

The effect of capping a dilute assembly of nanoscale mass-selected Fe clusters with a Co thin film has been studied using X-ray magnetic circular dichroism (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 to the bulk, by around 4% for mspin and around 75% for morb. In addition, a surface core level shifted component is observed in the L3,2 XMCD spectrum. Upon adding the Co layer, the surface component disappears, morb is decreased for the Fe clusters, and mspin increases. The exposed clusters are magnetically isotropic but a strong in-plane anisotropy is observed after depositing the Co overlayer. We attribute this to the shape of the Co islands in which the Fe clusters are embedded