Sintering and cooling atmosphere effects on the microstructure, magnetic properties and DC superposition behavior of NiCuZn ferrites

This study investigated the sintering and cooling atmosphere effects on the microstructure and magnetic properties of NiCuZn ferrites. The copper-rich phase segregated during sintering near the grain boundaries. The sample sintered in N2 and cooled in air (N2-Air) exhibited the highest amount of segregated copper-rich second phase, followed by the sample sintered and cooled both in air (Air-Air). However, no precipitate was observed for the sample sintered and cooled both in N2 (N2-N2). This can be explained by the fact that Cu2+ was reduced into Cu+, promoting Cu2O phase precipitation and then reacting with CuO to form a liquid phase. The Air-Air sample exhibited the highest initial permeability (μi ≈ 250) and saturation magnetization (Bs ≈ 88 emu/g), followed by N2-N2 (μi ≈ 180, Bs ≈ 82) and N2-Air (μi ≈ 150, Bs ≈ 80). The highest DC superposition behavior was obtained for N2-Air sample due to the highest nonmagnetic copper-rich precipitate thickness at the grain boundaries.