Study On Single Phase Or SrFe₁₂O₁₉ Dual-Phase Composite Magnetic Materials

In this paper,SrFe₁₂O₁₉ particles were prepared by sol-gel method,Co particles were prepared by sodium formate reduction method and solvothermal method,Fe-Co particles were prepared by solvothermal method.And then SrFe₁₂O₁₉ particles were used as hard magnetic phase to prepare SrFe₁₂O₁₉/Co or SrFe₁₂O₁₉/Fe-Co dual-phase composite particles by depositing Co or Fe-Co particles onto the surface of hard phase using electroless plating method,solvothermal method,and so on.The microstructure and magnetic properties were characterized by X-ray diffractometer,transmission electron microscopy,scanning electron microscopy,Fourier transform infrared spectroscopy,differential scanning calorimetry and vibrating sample magnetometer.The formation mechanism of hard magnetic SrFe₁₂O₁₉particles and soft magnetic Co were discussed.The effects of experimental parameters on microstructure and magnetic properties of single-phase particles and dual-phase particles were investigated.The main experiments and results are as following:（1）The pure SrFe₁₂O₁₉ particles were prepared by sol-gel method.The effects of solvent type,calcination temperature and holding time on the structure and magnetic properties and the formation mechanism of SrFe₁₂O₁₉ particles were studied.It is found that the solvent type and the calcination temperature significantly affect the morphology of SrFe₁₂O₁₉ particles.The rod-shaped SrFe₁₂O₁₉ particles can be obtained the best magnetic properties by using ethylene glycol as solvent and sintering at 900°C for 2 h,and the coercivity（Hc）,remanent magnetization（Mr）and remanence ratio（Mr/Ms）of that were7238.7 Oe,21.3 emu/g and 0.54,respectively.The Hc,saturation magnetization（Ms）and Mr/Ms of SrFe₁₂O₁₉/Fe₇Co₃ composite magnetic particles prepared by electroless plating method were 3715.5 Oe,61.1 emu/g and 0.36,respectively,when the SrFe₁₂O₁₉ particles were introduced into the precursor solution with Fe³⁺:Co²⁺=6.5:3.5.（2）The pure FCC-Co particles with a particle size of 0.1μm¹.0μm were prepared by sodium formate reduction method.The effects of Co²⁺concentration in the precursor solution on the microstructure and magnetic properties and the formation mechanism of the Co particles were investigated.The results show that Co particles have the best soft magnetic properties with Ms of 163.8 emu/g and Hc of 130.9 Oe when the concentration of Co²⁺is 0.036 mol/L.When the concentration of Co²⁺is 0.012 mol/L,the particle size of Co is the smallest（50 nm¹00 nm）.Hc and Ms of SrFe₁₂O₁₉/Co composite magnetic particles prepared by sodium formate reduction method were 1094.1 Oe and 57.0 emu/g,respectively,when SrFe₁₂O₁₉ particles were introduced to the precursor solution with Co²⁺concentration of 0.012 mol/L.（3）Co particles existed in FCC-Co and HCP-Co types were prepared by solvothermal method.The effects of sodium hydroxide and nucleating agent content on the structure and magnetic properties of Co particles were investigated.The results show when the sodium hydroxide is 0.8 g and the Ag⁺:Co²⁺is 1:100,the samples exhibit the best soft magnetic properties,namely,Hc=176.7 Oe and Ms=91.1 emu/g.SrFe₁₂O₁₉/Co composite particles were prepared by solvothermal method by introducing SrFe₁₂O₁₉ particles to the precursor solution with the content of sodium hydroxide of 0.8 and Ag⁺:Co²⁺of 1:100.It was found that Co cladding layer was dense and Co particle size was about 100 nm.The Hc,Ms and Mr/Ms of SrFe₁₂O₁₉/Co composite particles is 3303.3 Oe,68.1 emu/g and 0.32,respectively,and Hc and Ms increased by 66.8%and 16.2%,respectively,compared with the SrFe₁₂O₁₉/Co composite particles prepared by the sodium formate reduction method.