Influence of Composition and Oxygen Partial Pressure in Sintering Atmosphere on Microstructure and Magnetic Properties of Ni–Zn Ferrite for Thin Film Magnetic Recording Heads

Abstract

Ni–Zn ferrite is a promising material as the substrate for thin film magnetic recording heads. The influence of specimen composition and partial oxygen pressure (PO2) in sintering atmosphere (N2+O2) on the microstructure and magnetic properties of Ni–Zn ferrite has been investigated by SEM and XPS. The results obtained are summarized as follows.(1) ZnO precipitates were observed at the grain boundaries, especially at the triple points of the Ni–Zn ferrite specimen sintered at 1453 K for 10.8 ks under 20% PO2. Such precipitates, however, were not detected in the specimen sintered in the atmosphere whose PO2 was 25%.(2) Although the permeability (μ) and the resistivity (ρ) of the Ni–Zn specimens sintered at 1453 K for 10.8 ks under 10 to 100% PO2 increased with increasing PO2, both the loss coefficient (Q) and the relative loss coefficient (tan δ/μ) showed an optimum value under 20% PO2.(3) The 0.3 mol% increment of ZnO and the 0.3 mol% decrement of NiO than the conventional composition (Fe2O3: 49.7 mol%, ZnO: 32.6 mol%, NiO: 17.7 mol%) prevented ZnO precipitation on the Ni–Zn ferrite specimen sintered at 1453 K for 10.8 ks in air.(4) The HIP’ed specimen after sintered at 1423 K, 30 K lower than the conventional sintering temperature of 1453 K, in air showed neither ZnO precipitation nor pores.