Magnetism in assembled and supported silicon endohedral cages: First-principles electronic structure calculations

First principles electronic structure calculations on a free CrSi12 cluster, a (CrSi12)(2) dimer, and CrSi12 clusters supported on Si(111) surfaces have been carried out within a gradient corrected density functional formalism using a supercell approach. The ground state of CrSi12 is a Cr centered hexagonal biprism of Si atoms in which the Cr spin moment is completely quenched. As two CrSi12 motifs are brought together, they form different composite units depending on initial direction of approach and, in most cases, the composite cluster is found to have a net spin moment. Cluster assemblies obtained by depositing CrSi12 motifs on a Si(111) surface exhibit similar finite spin moments for several initial directions of approach. An analysis of the electronic states shows that the origin of the magnetic moment lies in those Cr d-states that do not mix with silicon sp states. The studies suggest the possibility of forming silicon-based magnetic semiconductors through such assemblies.