(Zn, Ni, Ti) substituted barium ferrite particles with improved temperature coefficient of coercivity

The Ba-ferrite particles have a positive temperature coefficient of dHc/dT. From the viewpoint of recording system applications, the dHc/dT should be reduced in order to improve the operating margin for temperature change. It was shown that the coercivity, Hc, of Ba-ferrite particles is mainly controlled by the crystalline anisotropy. In the Ba-ferrite there are five distinct crystallographic sites or sublattices, and the Fe3+ ion located on different site has different contribution to crystalline anisotropy. The replacement of Fe3+ ions by Zn2+, Ni2+, and Ti4+ ion will effect on the saturation magnetization σs, coercivity Hc and their temperature coefficients. The Zn–Ti, Ni–Ti, and Ni–Zn–Ti substituted Ba-ferrite particles were investigated. It was found that the Zn–Ti substituted Ba-ferrite particles have higher σs, but large temperature coefficient of coercivity dHc/dT. In the case of Ni–Ti and Ni–Zn–Ti substitution the dHc/dT could be reduced to a small value, near to zero or negative value, while the σs decreases very slowly with increasing the amount of substitution.