Magnetic structure of free iron clusters compared to iron crystal surfaces

Electronic and magnetic properties of free Fe clusters of 9 to 89 atoms are investigated theoretically within an ab initio fully relativistic framework and compared to results of crystal surfaces. It is found that the local spin magnetic moments μₛₚᵢₙ and the orbital magnetic moments μorb are enhanced for atoms close to the surface of a Fe cluster. The corresponding Friedel-like oscillations in the depth profiles of μₛₚᵢₙ and μorb are more pronounced for clusters than for crystal surfaces. The μₛₚᵢₙ in clusters and at crystal surfaces turned out to depend linearly on the effective coordination number Neff. This empirical μₛₚᵢₙ-Neff inter-relationship is able to account for some features of the experimentally measured dependence of the magnetic moment of free Fe clusters on the cluster size. The spin-polarized density of states (DOS's) for atoms in clusters is characterized by sharp atomiclike peaks and substantially differs from the DOS in the bulk. The width of the local valence band gets more narrow if one is moving from the center of the cluster to its surface. The DOS averaged over all atoms in a cluster converges to the bulk behavior more quickly with cluster size than the DOS of the central atoms of these clusters.