Engineering soft magnetic properties by doping ions in low-fired M-type hexaferrite with Bi–Co–Ti substitution

Abstract

M-type hexaferrite with appropriate Co, Ti and Bi co-doping has excellent soft magnetic properties in a very high frequency range and can be sintered at low temperatures. This paper systematically investigates the effect of these ion substitutions in different lattice sites for Ba_1−xBi_x(Co_x+yTi_y)Fe_12−x−2yO₁₉ (x = 0.05–0.3 & y = 1.0–1.2). Bi substitution promotes the sintering densification and lowers the sintering temperature by an approximate relation of T_s = 1150 − 1500x + 2500x², where a denser microstructure also works for higher permeability. Co substitution plays a key role in the magnetic properties through magnetocrystalline anisotropy. For all samples, the permeability always reaches a maximum when the Co amount (x + y) is around 1.2 because it has an appropriate planar magnetocrystalline anisotropy at such composition. This work can provide a clear guide for the design of magnetic materials at a very high frequency range.