The influence of impurities and vacancies on the formation of the magnetic

moment in CaB6 was investigated by using full-potential ab initio band-structure

calculations. The CaB6 was found to be a band insulator with a band-gap of about

0.2eV. The calculated results indicated that carbon and oxygen substitution in the

boron sub-lattice, usually arising from their presence as impurities in low-purity

boron, did not play a significant role in the local moment formation. On the other

hand, a boron vacancy in the boron sub-lattice led to the formation of an impurity

band, in the vicinity of the Fermi level, which exhibited a finite exchange splitting

and magnetic moment. This exposure of the role played by vacancies in the sublattice

responsible for electronic conduction was an important revelation in the

understanding of ferromagnetism in the dilute electron system.

Role of Vacancies and Impurities in the Ferromagnetism of Semiconducting CaB6.

K.Maiti: EPL, 2008, 82, 67006