Nickel-zinc microwave ferrite with stress-insensitive square hysteresis loop

By substitution of Mn3+ ions for 0.2 Fe3+ ions per formula unit of dense polycrystalline 5000-G Ni0.65Zn0.35Fe2O4, the hysteresis loop becomes square (remanent magnetization increases by a factor of 2) without deterioration of X-band microwave dielectric properties or significant increase in coercive field. In addition, the loop is rendered virtually insensitive to externally applied stress. The results are explained by the strong positive magnetostriction contributions from octahedral-site Mn3+ ions that cancel the negative magnetostriction of the NiZn ferrite. An energy balance model, based primarily on the extrinsic hysteresis loop parameters, is used to illustrate the dependence of remanent magnetization on magnetostriction, coercive field, and saturation magnetization. With this simple composition change, high magnetization NiZn ferrites can be stress-insensitive square-loop materials with superior ceramic and microwave dielectric properties.