Magnetism of cobalt nanoclusters on graphene on iridium

The structure and magnetic properties of Co clusters, comprising 26–2700 atoms, self-organized or not on the graphene/Ir(111) moire, were studied in situ with the help of scanning tunneling microscopy and x-ray magnetic circular dichroism. Surprisingly, the small clusters have almost no magnetic anisotropy. We find indication for a magnetic coupling between the clusters.