Effect of replacement of Fe~(2+) by Co~(2+) in W-type hexagonal ferrite BaFe_(18)O_(27) to its electronic properties from first principles

摘要

Using a model in which Fe at 6g sites is assumed to be partially replaced by Co, the electronic ground structure of BaCo_2Fe_(16)O_(27) and the origin of the electrical conductivity have been studied within framework of the generalized gradient approximation (GGA) plus Hubbard U (GGA+U) calculation. Replacement of Fe at 6g site of BaFe_(18)O_(27) by Co causes the mixed valence states of Fe cations at 6g sites to vanish and the charge carrier density to lower. This is the main reason why both of materials reveal high electrical conductive anisotropy and the electrical resistivity of BaCo_2-W is 10~3～10~4 times higher than BaFe_2-W.