Abstract. The size-dependent magnetic properties of small iron clusters deposited on ultrathin Ni/Cu(100) films have been studied with circularly polarized synchrotron radiation. For x-ray magnetic circular dichroism studies, the magnetic moments of size-selected clusters were aligned perpendicular to the sample surface. Exchange coupling of the clusters to the ultrathin Ni/Cu(100) film determines the orientation of their magnetic moments. All clusters are coupled ferromagnetically to the underlayer.

With the use of sum rules, orbital and spin magnetic moments as well as their ratios have been extracted from x-ray magnetic circular dichroism spectra. The ratio of orbital to spin magnetic moments varies considerably as a function of cluster size, reflecting the dependence of magnetic properties on cluster size and geometry. These variations can be explained in terms of a strongly size-dependent orbital moment. Both orbital and spin magnetic moments are significantly enhanced in small clusters as compared to bulk iron, although this effect is more pronounced for the orbital moment.

Magnetic properties of deposited clusters are governed by the interplay of cluster-specific properties on the one hand and cluster-substrate interactions on the other hand. Size dependent variations of magnetic moments are modified upon contact with the substrate.

Received 11 July 2002, in final form 14 October 2002
Published 12 December 2002