Role of vacancies and impurities in the ferromagnetism of semiconducting CaB6Kalobaran Maiti
Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research Homi Bhabha Road, Colaba, Mumbai - 400005, India
received 22 March 2008; accepted in final form 26 May 2008; published June 2008
published online 4 June 2008
We investigate the influence of impurities and vacancies in the formation of the magnetic moment in CaB6 using full-potential ab initio band structure calculations. CaB6 is found to be a band insulator with a band gap of about 0.2 eV. The calculated results indicate that carbon and oxygen substitutions in boron sublattice, usually expected as impurity in low-purity borons, do not play a significant role in the local moment formation. The boron vacancy in the boron sublattice, on the other hand, leads to the formation of an impurity band in the vicinity of the Fermi level, which exhibits finite exchange splitting and magnetic moment. All these results provide a remarkable representation of the experimental results. This finding of the role of vacancies in the sublattice responsible for electronic conduction is an important revelation in the understanding of ferromagnetism in the diluted electron system.
75.50.Pp - Magnetic properties and materials: Magnetic semiconductors.
71.55.-i - Electronic structure of bulk materials: Impurity and defect levels.
75.10.Lp - Magnetic properties and materials: Band and itinerant models.
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