The Function of Co in Co-substituted M-type Ferrites: ⁵⁹Co-NMR Study

Abstract

The uniaxial magnetic anisotropy of the magnetoplumbyte-type (M-type) hard ferrite magnet is improved by the substitution of small amount of Co for Fe. The Co atoms occupy at least 3 sites among 5 crystallographically inequivalent Fe sites. Different magnetic functions of Co are expected at the different sites because of different oxygen coordinations around the sites. We have revealed from ⁵⁹Co nuclear magnetic resonance experiment that only Co located at the tetrahedrally coordinated 4f₁ site is responsible for the enhancement in the uniaxial anisotropy, demonstrating that the control of the Co occupation site is essentially important in the Co-doped M-type ferrite. If only the tetrahedrally coordinated 4f₁ site were occupied by Co atoms, the magnetic performance can be improved more efficiently.