Fe/ni - Zinc Ferrite Soft Magnetic Composite Material And Application Research

With the CPU, FPGA and different types of chip ASIC development, low voltage-high current has become the development trend of DC-DC converters. Therefore, power inductors with resist high dc bias become the focus of the development.Soft magnetic composites had been the hotspot in the research field of high current power inductor materials because of its excellences such as high saturation magnetization, excellent dc bias characteristics, low magnetic loss and price. Presently, the investigation on preparation of the soft magnetic composites were mainly used non-magnetic insulator coating on the surface of bare Fe.The disadvantage is that the saturation magnetization decreases significantly, which results in a bad dc bias characteristics. In this thesis, high resistivity of Ni-Zn ferrite materials were used as insulator, so as to slightly decrease the saturation magnetization of soft magnetic composites and improve its dc bias characteristics.In this research, Fe/Ni-Zn ferrite soft magnetic composites were prepared by using high pure iron powder raw materials and chemical co-precipitation method. The effect of Ni-Zn ferrite formula and content varation on magnetic properties of Fe/Ni-Zn ferrtie soft magnetic composites were disscused.The contribution of domain-wall component and spin-motion component to the permeability spectra was estimated by the numerical fitting of actual measurement data using a least mean square method. Based on these results, toroidal inductors were prepared by the Fe/Ni-Zn ferrtie soft magnetic composites, and applied in Buck converter. The main research results are as follows:(1)For Fe/NixZn1-xFe2O4(x=0.1,0.3,0.5,0.7,0.9) soft magnetic composites, when x=0.7the saturation magnetization reachs maximum, which is about91%of that of bare Fe. When x=0.3the initial permeability reachs maximum, and the magnetic loss has the lowest value at the frequency scope of10-100KHz. However, at the frequency scope of200-1000KHz, the magnetic loss has the lowest value at x=0.1.The domain-wall component makes major contributions to the permeability spectra.(2) For Fe/Nio.3Zno.7Fe2O4(1,2,3,5,6Wt%) soft magnetic composites, with the incresaing of mass fraction of Nio.3Zno.7Fe204, the saturation magnetization is linearly decreased.When the mass fraction of Nio.3Zn0.7Fe2O4is1Wt%, the saturation magnetization is about96%of that of bare Fe.When the mass fraction of Nio.3Zno.7Fe2O4is6Wt%, the saturation magnetization is about90%of that of bare Fe. The magnetic loss increases at first and then decrease at the frequency range of10-100KHz.When the mass fraction of Nio.3Zn0.7Fe2O4is2Wt%, the maximum values were obtained. However, at the frequency range of200-1000KHz, the magnetic loss is rapidly decreased.The major contributions to the permeability spectra varies gradually from the domain-wall component as the main to spin-motion as the main.(3) The efficiency of Buck converter is75%at rated load and it is worth to be applied.