Preparation And Magnetic Properties Of Hexagonal M-type Strontium Ferrite-based Composites

M-type SrFe₁₂O₁₉（SrM）ferrite has been widely studied and applied because of its large uniaxial magnetocrystalline anisotropy,good chemical stability and low production cost.At present,the exchange coupling between the hard magnetic phase and the soft magnetic phase is one of the effective methods to improve the magnetic properties of hard magnetic materials.Compared with the hydrothermal method commonly used before,chemical co-precipitation method is more suitable for the mass preparation of powder.Therefore,it has important practical value to study the preparation of composite ferrite powders by chemical co-precipitation method.In this thesis,chemical co-precipitation method was used to prepare Sr M/NZFO（S/NZ）and Sr M/CFO（S/C）composite ferrites,with Sr M ferrite as hard magnetic phase and Ni_0.6Zn_0.4Fe₂O₄（NZFO）ferrite and Co Fe₂O₄（CFO）ferrite as soft magnetic phases.The effects of different compositions and aligning magnetic field on the structure,magnetic properties and exchange coupling of composite ferrites were studied.The study of SrM/NZFO composite ferrite samples shows that only Sr M and NZFO phases existed in the composite samples sintered at 1100℃,and there is an obvious exchange coupling interation.When the Sr M content of the samples sintered at 1200℃is85%,the third phase of W-type Sr（Ni Zn）Fe₁₆O₂₇（Sr W）ferrite began to appear obviously,and there is also exchange coupling found in the samples.The magnetic properties of the composite ferrites prepared at the two sintering temperatures abided by the same change rules.In the Sr M/NZFO samples,the M_s of the composite samples increased,while the H_cdecreased with the increasing conent of NZFO.It was found that the M_s of Q-S/NZ composite ferrites with a forming aligning magnetic field was increased at two sintering temperatures,but the significant increase of H_c was only found in the samples sintered at1200℃.The study of SrM/CFO composite ferrite samples shows that the third phase did not appear in the samples sintered at 1200℃,and there was an obvious exchange coupling between the soft and hard magnetic phases.In Sr M/CFO samples without aligning,the saturation magnetization M_s increased,while the coercive force H_c decreased with the increasing content of CFO.The Q-S/C composite ferrites with a 640 k A/m forming aligning magnetic field had the same variation law of magnetic properties with S/C ferrites.In addition,the M_sand H_c of Q-S/C samples were improved to a certain degree compared with those of S/C samples with the same composition.