ホットプレスによるフェライトの製作とその性質

抄録

This paper describes the sintering process of ferrites under hot pressing and their magnetic properties. Bulk density ρ and grain growth aspect were investigated as a function of the maximum firing temperature T_m and the hot pressing pressure at T_m (P_h) in the case of Ni_0.3 Zn_0.7 Fe₂O₄ and Cu_0.4 Zn_0.6 Fe₂O₄ and compared hot pressed specimen with the specimen obtained by conventioned firing method. From ρ-T_m curves of CuZn and NiZn ferrite, we can see that the specimen prepared by the conventional method shows anomalous expansion in the sintering process. However, in the case of hot pressing, no expansion phenomenon was observed and the densification was considerably promoted. As the result, we could obtain the specimen with same density as the conventionally sintered one under hot pressing at lower temperature by 200°C than the ordinary firing. The effect of hot pressing on grain growth was examined by means of an electron microscope. The result shows that hot pressing greatly obstructs grain growth. The magnetic properties of the hot pressed ferrite differed from that of the ordinary fired ferrite. Especially, in the NiZn ferrite, the decrease of initial permeability μ and altered temperature characteristic of μ were the result of hot pressing. And, in the hot pressing case, lower maximum flux density B_s and higher coercive force H_c were also obtained as compared with that prepared by the conventional method. Measurement on the ferromagnetic resonance was carried out on NiZn specimen at 6790Mc. From this result we can see that the static magnetic field required for resonance H_c decreases and the magnitude of line width ΔH increases considerablly by hot pressing.