Copper-rich phase segregation effects on the magnetic properties and DC-bias-superposition characteristic of NiCuZn ferrites

NiCuZn ferrites with Ni_0.42Cu_0.13+xZn_0.45Fe_2-xO₄; x=0, 0.01, 0.02, 0.04, 0.07, 0.1 chemical compositions were prepared using conventional solid-state reaction in this study. The effects of different NiCuZn ferrite chemical compositions on the microstructure, magnetic properties and DC superposition characteristics were investigated. The results showed that increasing the CuO content in the NiCuZn ferrites led to copper-rich phase precipitation at the grain boundaries. The liquid phase resulted from copper-rich phase melting during sintering, promoting liquid phase densification and hence lowering the maximum densification rate temperature. The non-magnetic copper-rich secondary phase at the grain boundaries reduced the effective magnetic field applied on the ferrite grain, and hence enhanced the DC superposition characteristics at low magnetic field. The sample with x=0.07 sintered at 1100 °C for 2 h exhibited excellent initial permeability (μ′=325) and superior DC superposition characteristics. A NiCuZn ferrite with superior initial permeability and DC superposition characteristics can be obtained by changing the x value to adjust the non-magnetic copper-rich precipitate thickness at the grain boundaries.