Magnetic moments, exchange coupling, and crossover temperatures of Co clusters on Pt(111) and Au(111)

The influence of cluster size and of cluster-substrate interaction on the magnetic properties of Co clusters of 1-10 atoms on Pt(111) and Au(111) is studied by fully relativistic ab initio calculations. The focus is on systematic trends of the spin and orbital magnetic moments, the exchange coupling, and the crossover temperature. The spin magnetic moments of Co clusters are larger for the Pt substrate than for the Au substrate, while the reverse is true for the orbital magnetic moments. The local magnetic moments of Co atoms generally increase if the number of Co neighbours decreases. The exchange coupling constants J(ij) depend on the cluster size and on the location of respective atoms. The crossover temperature increases monotonically with cluster size and is larger for clusters on Pt than for clusters on Au.