Preparation And Regulation Of Magnetic Properties For The Co-based Soft Magnetic Materials

Soft magnetic materials are widely used in the fields of energy transportation,aviation shipping,electronic information,microwave absorption,biotechnology and high frequency because of their high saturation magnetization(Ms),high permeability(?)and low coercivity(Hc).In the recent years,with the rapid development of communication technologies,the demand for soft magnetic materials has increased year by year.It is a trend to find some methods with low energy consumption and simple preparation process.Zr_6-xHf_xCo₂₃(0?x?6),FeCo,and FeCo@CoFe₂O₄ series of soft magnetic single phase and soft/hard magnetic composites were prepared by the solid phase method and the organic high temperature liquid method,respectively.The effects of doping and various reaction conditions on the structure and magnetic properties of the synthesized materials were studied,the conclusions are as follows:(1)M₆Co₂₃(M=Zr,Hf)magnetic materials were synthesized by simple solid-phase sintering using Zr,Hf and Co powders.The oxidation of Zr and Hf can be prevented when the double reducing agents are used.The saturation magnetizations of Zr₆Co₂₃and Hf₆Co₂₃ pure phase soft magnetic materials are up to 72.38 emu/g and 41emu/g.Both of them exhibit room-temperature soft magnetic properties with the curie temperatures up to500?.The single phase Zr_6-xHf_xCo₂₃(0<x<6)solid solution can be prepared by the combination of ball milling pre-treatment and solid phase method.The ball milling process can effectively promote the solid solution reaction.The saturation magnetization of the Zr_6-xHf_xCo₂₃(0<x<6)single-phase solid solution prepared through ball milling of8h is between 58.26 emu/g and 66.82 emu/g,in agreement with the solid solution properties.Zr₃Hf₃Co₂₃ solid solution shows a optimal thermal stability,and its properties tend to be more stable at a higher temperature.(2)Soft magnetic FeCo nanomaterials were synthesized by high temperature organic liquid-phase reaction using Fe(acac)₃ and Co(acac)₂ as reaction sources.The morphology and magnetic properties of FeCo magnetic nanoparticles were regulated by reaction temperature,heating rate,reaction time and stirring rate.The preparation conditions of monodisperse FeCo nanoparticles with maximum saturation magnetization are stirring rate of 300 r/min,reaction temperature of 340?,reaction time of 2 h,and heating rate of3?/min.Its saturation magnetization increased from 147 emu/g to 215 emu/g after annealing,which is 97%of the saturated magnetization for the FeCo bulk.(3)Fe(acac)₃ and Co(acac)₂ were used as precursors to synthesize CoFe₂O₄magnetic nanoparticles,their magnetic properties and morphology were regulatedby reaction temperature and surfactant.CoFe₂O₄ nanomaterials with higher saturation magnetization and larger coercivity are easily prepared at higher reaction temperature.The coercivity can be greatly enhanced after annealing.The morphology can be regulated as spherical and cubic nanocrystalline structures by surfactants.Taking FeCo nanoparticles with the size of 15 nm as the cores,FeCo@CoFe₂O₄soft/hard magnetic composite nanostructures were synthesized by seed method,the morphology is polyhedral and its diameter is about20 nm.The magnetic coupling occurs at the two-phase interface due to the soft/hard magnetic diffusion after annealing.The coercivity and saturation magnetization are 640Oe and 119 emu/g,respectively,which is between the soft magnetic single-phase and the hard magnetic single-phase.This result is due to the magnetization reversal of the thin CoFe₂O₄ hard magnetic drived by the thicker FeCo soft magnetic field in the low field.In conclusion,a series of Co based soft magnetic materials of Zr_6-xHf_xCo₂₃(0?x?6),FeCo and FeCo@CoFe₂O₄ were prepared by solid phase method and high temperature organic liquid phase method,respectively.The optimal synthesis conditions were obtained by exploring a series of reaction conditions.These results will provide some experiment foundations for the study of Co based soft magnetic materials.