Influence of Cu substitution and Bi2O3 doping on magnetic properties of low-temperature-fired NiCuZn ferrites

Two groups of low-temperature-fired Ni0.6-xZn0.4CuxFe1.98O4 (x = 0.1-0.325 in intervals of 0.025) under two different doping modes, namely, low, i.e., group A with 0.25 wt% Bi2O3 and high, i.e., group B with 1 wt% Bi2O3, were prepared by solid-state reaction method. Their crystal phase composition, microstructure, and soft magnetic properties were studied and compared. The series of ferrite samples of both groups presented single spinel ferrite phase. However, average grain sizes of samples in group A were significantly smaller than those in group B. Microstructures of samples changed significantly with the increase in Cu content. Furthermore, relative density, permeability, saturation flux density (Bs), and quality factor, first increased and then decreased with increasing Cu content, in both groups. Snoek constants in the two groups increased monotonously. However, densified samples in group A had higher Snoek constants than samples in group B, which indicated that they were more suitable for high-frequency applications. In general, overall performance of samples in group A was better than that of samples in group B, but properties of the former were more sensitive to Cu content. Therefore, to achieve better overall performance, it was best to choose samples with proper Cu substitution (x = 0.275) in group A. For improved robustness of ferrite composition and process, it was more appropriate to choose samples with proper Cu substitution ((x = 0.25) in group B.