Spin and orbital magnetization in self-assembled Co clusters on Au(111)

We show that superparamagnetic Co clusters supported on a Au(111) surface exhibit a strong variation in perpendicular magnetic anisotropy with cluster size, which can be ascribed to electron localization at the perimeter of the clusters. The reduced dimensionality of such sites leads to drastic changes in the $3d$ electronic structure resulting in an increased orbital magnetic moment and a temperature-dependent $3d$ band occupancy.