Pressure sintering of MnZn and NiZn ferrites

Polycrystalline MnZn and NiZn ferrites suitable for recording-head applications have been prepared by pressure sintering (hotpressing). General conditions for pressure sintering and details of the apparatus are described. Also discussed are the effects of grain size and temperature, in the normal range of glass bonding, on the magnetic and physical properties of pressure-sintered MnZn ferrite. It was observed that the strength of the ferrite increased with decreasing grain size in the range studied (15 to 500 μm). An opposite effect was noted for resistance to material wear. Increases in permeability up to 30 percent were obtained by relieving residual machining stresses with anneals in the 500 to 900°C range. Similar increases in strength were observed for low-temperature anneals. However, at temperatures higher than 500°C, the strength was reduced strongly, with the amount of the reduction being dependent upon the surface finish of the ferrite and its geometry. In general, strength was reduced with coarser surface finish and increasing surface-to-volume ratios. Data on material wear and hardness as functions of grain size and composition are presented. Improvement in performance of video recording heads fabricated of pressure-sintered MnZn ferrite as compared to Alfesil and single-crystal MnZn ferrite is also demonstrated.