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

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, ins 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 mL corresponds to an increase of similar to 75% relative to bulk Fe. Coating the Fe clusters with Co further raises their magnetic moments, as a result of the increases in ms across the size range. For the 180-atom clusters, m(S) is 20% greater than in the bulk. (C) 2002 Elsevier Science B.V. All rights reserved.