Magnetic anisotropy of nanoscale cobalt particles

We report calculations of the magnetic anisotropy energy (MAE) of cobalt nanoparticles in the size range 300-1000 atoms. The MAE is expressed in terms of shell-resolved contributions from different parts of the cluster. The net anisotropy is a delicate balance between contributions from the interior and the surface of the cluster that generally have opposite signs. We study closed shell structures for which the MAE is fourth order in the spin-orbit coupling, and clusters for which additional layers have been added to the facets, inducing uniaxial anisotropy. Both Co and Cu facet additions are considered. The relation of the results to experimental work is discussed.