Hot-pressed Mn-Zn-Ni and Mn-Zn-Co ferrites for magnetic recording heads

Ni²⁺ and Co²⁺ substituted Mn-Zn ferrites have been developed as high-density magnetic recording materials by hot pressing using optimum sintering parameters. Ferrite series of the composition Mn_0.6Zn_0.4-xNi_xFe₂ O₄ and Mn_0.6Zn_0.4-yCo_yFe₂O₄ were prepared by the hot-pressing technique wherein x and y varied from 0.0 to 0.4 in steps of 0.05. It yielded ferrites with improved magnetic properties having higher hardness (⩾650 Vickers units), low porosity (<0.1%), and small grain size (≈10 μm). The initial permeability increased, whereas the coercive field decreased for an Ni²⁺ concentration x or a Co ²⁺ concentration y equal to 0.05. Maximum values of saturation magnetization equal to 4850 and 5250 G were obtained for x and y equal to 0.225 and 0.275, respectively. The Curie temperature increased appreciably, whereas the DC resistivity decreased for a larger substitution of Ni²⁺ and Co²⁺ ions