Research And Preparation Of Low Loss Power Ferrites Used At High Frequency

The development of information technology puts higher requirements on the devices used for power transmission.For the high-frequency,miniaturization and lighter requirements of devices,soft magnetic materials with low power loss and superior performance have become a hot topic.Among all soft magnetic materials,metal soft magnetic material can only be applied at lower frequencies because of its low resistivity and large eddy current loss.At 1 MHz and above,ferrite is the most industrialized power transmission soft magnetic materials.In this paper,ferrite used above 1 MHz was prepared using solid oxide sintering process.MnZn power ferrite that can be used at 5 MHz is prepared by optimizing the sintering process,the selection of the main component,the action of a single additive and the ionic combined replacement method.Then NiZn ferrite was synthesized by optimizing the appropriate ratio of distribution.The conclusions are as follows:1)The addition of NiO in MnZn ferrite can significantly improve the temperature characteristics of power loss,the main reason is that its addition can improve the cutoff frequency of materials.Because of its better diffusion effect,nano-NiO can suppress grain growth in the early stage of grain growth,and has a better effect on the improvement of the cutoff frequency and the reduction of residual loss.2)The addition of In2O3 in MnZn ferrite can improve the compactness of sintering and significantly improve the saturation magnetic induction.Therefore the magnetic permeability of MnZn ferrite can be effectively improved under a certain cutoff frequency.In addition,the addition of In3+ also reduces the anisotropy constant and magnetostriction of ferrite,and the conduction mechanism inside the crystal grains can be suppressed,thereby increasing the resistivity inside the grains and reducing the power loss under high frequency.3)Polycrystalline MnZn ferrites used at frequency higher than 5 MHz were obtained by conventional solid-state reaction.By adding multiple additives as Ca,Si,Ti,In and Ni in appropriate main composition,power loss of the optimal MnZn ferrite is 84.4kW/m3 at 3 MHz,10mTunder 100℃,117.9 kW/m3 at 5 MHz,5 mT under 100℃ measured by BH analyzer,and the rate of power loss change is less than 35%from 25℃ to 120℃.From the magnetic spectrum measured by Impedance/Material Analyzer,the resonance of domain wall is confirmed to be the reason of cut-off frequency for MnZn ferrite.We put forward a method to prepare power ferrites used at higher frequency by multiple additives and utilizing the synergistic effect on magnetic spectrums and core losses among different elements.4)From the comparison of magnetic spectrum and power loss,one conclusion can be drawn that with the domain wall resonance get stronger at cut-off frequency,power loss become lower at high frequency.It is also found that the resonance peak of MnZn ferrite prepared by the ion combination replacement method is obviously enhanced,and the power loss is also reduced.