Magnetic anisotropy of a single cobalt nanocluster

Using a new micro-SQUID setup, we investigate magnetic anisotropy in a sing le 1000-atom cobalt cluster This system opens new fields in the characteriz ation and understanding of the origin of magnetic anisotropy in such nanopa rticles. For this purpose, we report three-dimensional switching field meas urements performed on a 3 nm cobalt cluster embedded in a niobium matrix. W e are able to separate the different magnetic anisotropy contributions and evidence the dominating role of the cluster surface.