Effects of SnO2 on DC-Bias-Superposition Characteristic of the Low-Temperature-Fired NiCuZn Ferrites

The microstructure and magnetic properties, especially the dc-bias-superposition characteristic of the SnO₂-doped and low-temperature-fired NiCuZn ferrites, were investigated. X-ray diffraction patterns displayed a single-phase spinel structure for all samples. In addition, with the increase of SnO₂ content, the average grain size, sintered density, and saturation magnetic flux density (B_s) gradually decreased. Initial permeability and Q-factor value first increased slightly, and then decreased continuously with further increasing SnO₂ content. Under relatively low superposition magnetic field (H <; 140 A/m), a higher initial permeability favored to obtain a higher incremental permeability. However, when the superposition magnetic field continued to increase, some samples with a lower initial permeability displayed a higher incremental permeability. The incremental permeability was mainly determined by B_s, especially coercivity (H_c) of the samples. The sample with 0.75 wt% SnO₂ favored to obtain a better DC-bias-superposition characteristic on incremental permeability and H_70% (the value of the superposition magnetic field when the incremental permeability reduced to 70% of the initial value). Possible mechanisms contributing to the above results were discussed in detail.