Zhongwen Lan

Grain growth, densification and magnetic properties of NiZn ferrites with Bi2O3 additive

The grain growth, densification and magnetic properties of Bi2O3 doped NiZn ferrites prepared by a solid-state reaction method were investigated. Addition of a moderate content of Bi2O3 additive, to NiZn ferrite, due to its liquid phase sintering enhanced the diffraction intensity while excessive content of Bi2O3 produced a thick liquid phase layer at the grain boundaries and retarded mass transfer during sintering. Thus the x-ray diffraction peaks exhibited reduced intensity. In samples with higher additive content, Bi2O3 segregated at the grain boundaries as a liquid phase layer. This phenomenon could be confirmed by backscattering electron image. The grain growth of Bi2O3 doped NiZn ferrites was discussed by using the liquid phase sintering mechanism. Bi2O3 promoted grain growth via liquid phase sintering, and the addition of the optimum content of Bi2O3 could enhance the density of the sample and reduce its porosity. The NiZn ferrite samples containing x = 0.20, 0.08 and 0.04 sintered at 1180 °C, 1220 °C and 1250 °C, respectively, exhibited high permeability (μi) and low core losses (PL) at 50 kHz and 150 mT. The losses here were composed mainly of hysteresis loss, both eddy current loss and residual loss were ignored. The addition of proper content of Bi2O3 can improve the saturation induction (Bs) and reduce the coercivity (Hc) by liquid phase sintering.

Effect of Ti-Substitution on temperature dependence and magnetic disaccommodation of MnZn ferrites

Ti-Substituted MnZn ferrites were prepared by the conventional ceramic process. The effects of Ti-Substitution on temperature dependence and magnetic disaccommodation of MnZn ferrites were investigated. The experimental results show that the valley between peak I and Peak II of the μi-T curve initially becomes flatter with higher Titanium content. However, if increasing Titanium content continually, the valley becomes steep eventually. Furthermore, at the same temperature section of the valley, an initial decrease followed by a subsequent increase in the intensity of peak II of disaccommodation spectra is observed with the increase in Titanium content. The valley becomes flatter when the peak II of disaccommodation spectra goes down. MnZn ferrite with low peak II of disaccommodation spectra and high thermal stability is achieved when the substitution of Ti4+ is 0.1 mol%.

Effect of annealing parameters on the magnetic properties of NiZn ferrite thin films

Ni0.5Zn0.5Fe2.0O4.0 thin films (NZFs) were deposited on Si (100) substrate by a sol–gel method, and the effects of annealing parameters on the structure and magnetic properties of the proposed films were investigated. Moderate heating rate was beneficial to the nucleation of NZFs. When the heating rate was 2xa0°C/min the saturation magnetization (Ms) achieved its maximum and the coercivity (Hc) reached its minimum. Both the crystallization and Ms of NZFs enhanced with increasing annealing time; however, Hc changed contrarily. High quenching temperature produced a large stress and consequently deteriorated magnetic properties. The optimal annealing parameters of NZFs were annealed at 700xa0°C, heating rate 2xa0°C/min, annealing time 1xa0h, and gradually cooled to room temperature. Finally, NZFs showed a high magnetization of 320xa0emu/cm3 and low coercivity of 86 Oe.