Preparation And Characterization Of Finemet/NiZn Ferrite Soft Magnetic Composites

To satisfy the developmental requirements of electronic miniaturization and high-frequency,it is need to exploit the new soft magnetic materials,which possess high permeability,high saturation magnetization and low loss.In this paper,according to the advantage of magnetic alloys and ferrite,the core-shell structured magnetic composites were prepared by the chemical co-precipitation method on the surface of FeSiNbBCu?Finemet?alloys,and ferrite as the insulation layer.The phase of ferrite was surveyed by X-ray and the microstructure characterization of ferrite was observed by scanning electron microscopy,magnetic properties were analyzed by LCR meter and VSM.Core-shell structured soft magnetic composites with the excellent properties were prepared by controlling constituent and prepared conditions.Spinel structure ferrites nanoparticles were prepared by using the improved chemical co-precipitation method.Suitable precipitant will contribute to the precipitation of ferrite precursor nanoparticles and Finemet alloy,NaOH as precipitant was more appropriate compare with ammoniaque,because particles of the precursor were small and uniform.In addition,the appropriate dispersant can effectively control the size and aggregation of the nanoparticles,the results showed that dispersion of the ferrite precursor particles was not obvious,and the particles appear part of aggregation without polyethylene glycol?PEG?,after add 3wt%of polyethylene glycol?PEG?,the precursor particle have well dispersion.With the increase of Zn content?x?,the MS of magnetic core present increase before decrease,the experimental results show that comprehensive magnetic properities was better compared with other content,such as Ms up to 87.2emu/g,when x was 0.5.And oxygen partial pressure to adjust crystal internal ion valence and good stability,when the oxygen content at 5?10%,NiZn ferrite nanoparticles have good microstructure and comprehensive magnetic properities.Core-shell structure Finemet/Ni_0.5Zn_0.5Fe₂O₄ composites core was prepared by chemical co-precipitation method.Using FeCl₃·6H₂O,ZnCl₂ and NiCl₂·6H₂O as raw materials to preparate NiZn ferrite precursors,NaOH as precipitant,after cold pressing,furnace sintering,the core-shell structure Finemet/NiZn ferrite soft magnetic composites were preparated.Study on the content of ferrite insulating layer,the pressure process of the composite,the sintering temperature,and oxygen partial pressure.And phase composition,morphology,and the rule of magnetic performance were discussed.With increase of ferrite content,the thickness of shell increase,which lead to permeability and saturation magnetization of the core reduce and the core loss also decrease.When oxygen partial pressure increases,crystallization of ferrite had improve,when oxygen partial pressure exceed 10%,the surface appears obvious crack even drop,and the permeability and saturation magnetization showed a trend of decreases before increase first,and core loss was inverse tendency.In addition,raising appropriately the pressure in the forming process of composite materials can improve the density of magnetic core,which can facilitate magnetic comprehensive performance.As temperatures continue to increase,magnetic properties of composite reduce inversely,and with increase of thickness of insulated layer and oxygen partial pressure increases,magnetic properities of composite also reduce gradually.Experimental results show that insulating layer of ferrite thickness was 1?1.5?m,oxygen partial pressure at 10%,the moulding pressure at 1400MPa,and the heat treatment temperature at 600 ?,the prepared Finemet/Ni_0.5Zn_0.5Fe₂O₄ composite show an excellent microstructure and magnetic properities,such as permeability up to 61.6,saturation magnetization was 135.5emu/g and lower composite core loss down to 1.51 w/Kg under the condition of 50mT in 100kHz.