Study On The Preparation And Magnetic Properties Of Nano-composite Magnetic Materials

Magnetic energy product of traditional permanent magnet is close to the theoretical value,the magnetic property of nano-composite magnetic materials can be greatly increased by exchange coupling interaction between hard and soft phases.In this paper,Sm-Co particles broken by high-energy ball mill and SrFe₁₂O₁₉ porous films which were prepared by sol-gel processing and dip coating technique were chosen as the hard phase of composite materials,Sm-Co/Co?Fe-Co?composite particles and SrFe12O19/Fe-Co composite films were synthesized with Co?Fe-Co?particles deposited onto the surface of hard phases by polyol process,electroless deposition and solvothermal method.The microstructure and magnetic properties of the obtained particles were characterized by the XRD?TEM?SEM?DSC and VSM instruments.Meanwhile,the reaction mechanism of different ways and the influence of experimental parameters for the microstructure and magnetic properties of the composite materials were studied,which provided some experimental bases and theoretical references for the preparation of nano-composite magnetic materials.It was found:?1?Pure Co particles which exist in hcp-and fcc-crystal structures were synthesis by polyol method.The reduction mechanism of polyhydric alcohol and the influence of Co²⁺concentration on the structure of product were researched.Founding that the Co²⁺concentration had a great influence on the phase composition.Sm-Co/Co composite particles were synthesized by introducing Sm-Co particles into the precursor solution,whose major magnetic parameters were as follows:H_c=311.4 Oe,M_r/M_s=0.087.?2?Pure Co particles with single fcc-Co structure were prepared by electroless deposition.The formation mechanism of fcc-Co particles and the influence of experimental parameters on Co particles were analyzed.The grain size of Co was decreased to 100 nm when the Co²⁺concentration was 0.108 mol/L.The content of PVP had some influence on the magnetic properties of Co particles and the reaction time affected the purity of product.Sm-Co/Co composite particles were prepared with Sm-Co particles introduced into the precursor solution.The remanence ratio of them was not improved,because the exchange coupling between hard and soft phase was weak.?3?Fe-Co particles with different structures were prepared using solvothermal methods by bring Fe³⁺and Co²⁺solution with different molar ratios to the high pressure reactor.Results showed that Co²⁺could induce the deposition of Fe³⁺,the M_s gradually raised and the content of?Fe,Co?₃O₄ decreased with the molar ratio of Fe³⁺/Co²⁺was decreased.The magnetic properties of product including Sm-Co/Fe-Co and oxide was unsatisfactory,because of the restrictions of exchange coupling between hard and soft magnetic phase.?4?SrFe₁₂O₁₉9 porous films were synthesed by sol-gel process and dip coating technique.When reaction time of sol rubber reached 20 min and dipping time of PS template was 10 s,the alveolate structure of SrFe₁₂O₁₉9 films could be observed.Combined with chemical reduction methods,SrFe₁₂O_19/Fe-Co composite films were achieved and their major magnetic parameters were as follows:H_c=1896.2 Oe,M_r/M_s=0.367.