Co–Ti co-substitution of M-type hexagonal barium ferrite

This paper reports a study of Co–Ti equiatomic co-substitution of M-type hexagonal barium ferrites Ba(CoTi)xFe12−2xO19, with the objective to adjust coercivity to meet different application requirements. The ferrites, with x = 0.00−1.30, all exhibited the single-phase M-type barium ferrite structure. At x = 1.30, the saturation magnetization (MS) decreased by 27.7% to 47.5 Am2 kg−1 and the coercivity (HC) decreased from 4047 to 171 Oe, providing a wide control range of coercivity. Complex magnetic permeability (μ' and μ'') was measured to be μ'max = 25 and μ''max = 1.5 (at 10 MHz). The value of μ' is much higher than that of un-doped barium ferrite (x = 0.00). Co–Ti substitution reduced the coercivity whilst increased magnetic permeability. These improvements in magnetic properties are attributed to Co and Ti occupancies at different sites in the barium ferrite crystalline structure. Substitution is preferred at 4f2, 2b and 2a sites at x < 0.50, but 2a and 4f1 sites at x < 1.15. In addition, the bulk density (ρ) of the sintered compound was found to increase with increasing Co–Ti substitution.