Enhancements in magnetic moments of exposed and Co-coated Fe nanoclusters as a function of cluster size

Abstract

X-ray magnetic circular dichroism has been used to measure the magnetic moments of exposed and Co-coated Fe nanoclusters in the size range 180–690 atoms. The clusters were deposited in situ onto highly oriented pyrolytic graphite substrates using a ultra-high vacuum-compatible gas aggregation cluster source. Enhancements in both the spin and orbital magnetic moments, m S and m L, respectively, are observed for the exposed clusters. As the cluster size is reduced, m S gradually increases from the bulk value, and for the 180-atom clusters, it is enhanced by around 10%. The degree of enhancement in m L also increases as the cluster size decreases, although m L starts to decrease again for the 180-atom clusters; the maximum value observed for m L corresponds to an increase of ∼75% relative to bulk Fe. Coating the Fe clusters with Co further raises their magnetic moments, as a result of the increases in m S across the size range. For the 180-atom clusters, m S is 20% greater than in the bulk.