The effect of post-heat treatment on structure, magnetic and mechanical properties of hot isostatic pressed (HIP) NiZn ferrite

The effects of hot isostatic pressing (HIP) and post-heat-treatment on the structure and the magnetic and mechanical properties of NiZn ferrites were studied. It was found that magnetic and mechanical properties of NiZn ferrites were degraded in the HIP process. X-ray diffraction analysis and magnetic measurements showed that the equilibrium oxygen content of the NiZn ferrites changes during the HIP process, and part of the spinel phase in the surface layer of the sample is decomposed into oxides (Fe₂O₃, ZnO, etc.). This leads to a decrease of both the soft magnetic (permeability, B- H loop) and mechanical properties (microhardness, H _ν, and bending strength, σ_f) of the NiZn ferrites. Therefore, in order to obtain uniform oxygen content and remove the strains from the HIP ferrites, suitable postannealing is indispensable. An HIP ferrite, Ni_0.32Zn_0.68Fe₂O₄, with B₁₀=3100 G, H_c=0.19 Oe, μ´ (1 MHz)=1400, σ_f=21 kg/mm², and H_ν=850 was obtained