Ni–Ti equiatomic co-substitution of hexagonal M-type Ba(NiTi)xFe12−2xO19 ferrites

Abstract

Ionic substitution is considered the most effective way to expand the operational frequency of barium hexaferrites. So far, little attention has been paid to high level substitutions and their impacts on low temperature sintering behavior. Here, co-substituted equiatomic Ni–Ti M-type barium ferrites of nominal compositions Ba(NiTi)xFe12−2xO19 (x = 0.30, 0.60, 0.90, 1.20) were prepared by a solid state reaction method and studied for their structural, and static and high frequency magnetic properties. It was found that the phase purity of M-type hexagonal barium ferrite does not depend upon the amount of Ni–Ti substitution investigated here. Concomitantly, Bi2O3 additives are shown effective in lowering the sintering temperature of hexaferrite materials. For low temperature processed samples, the addition of Bi2O3 enables improved densification from localized liquid phase formation and restricted grain growth from its colocation at grain boundaries. By comparing samples and process conditions, the effect of grain growth and sintering aid upon sample microstructure, bulk density (ρ), saturation magnetization (Ms), coercivity (Hc) and magnetic permeability (μ′ and μ″) is made clear.