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.