High Pressure Synthesis and Physical Property Measurements of R-type Hexagonal Ferrite-Structure Oxides BaFe_xCo_6-xO₁₁ (0 ≦ x ≦ 4)

Abstract

Single phase samples of a cobaltite BaCo₆O₁₁ and its Fe-substituted derivatives BaFe_xCo_6-xO₁₁, which have R-type hexagonal ferrite structures, were successfully synthesized by a high-pressure and high-temperature method. BaCo₆O₁₁ was found to be a ferromagnetic metal. Mixed valent Co^3.4+ cations at the octahedral B(1) and B(2) sites contribute to the metallic conduction, whereas Co³⁺ cations at the trigonal-bipyramidal B(3) site give local magnetic moments, which order ferromagnetically below the Curie temperature of 17 K. The Fe substitution largely increases the magnetic transition temperature and changes the ground state to a ferrimagnetic semiconductor owing to the introduction of localized Fe³⁺ cations at the B(1) and B(2) sites.