Preparation, Structure, Morphology And Magnetic Properties Of M-type Ferrite Powders And Sintered Magnet

As a kind of important permanent magnetic materials, M-type permanent magnetic ferrites are widely applied in the fields of electronics industry and heavy industry. In this paper, the preparations, structures, morphologies, and magnetic properties of M-type permanent magnetic ferrites have been studied from the aspects of ions substitution and preparation methods. The major results of this paper are as follows:1. The magnetic powders of BaM partly replaced by Zn-Ti were prepared via the molten-salt growth method and investigated by Zn-Ti percentage and different cosolvents. We found that the change of HcI not only dependent on Zn-Ti percentage, but also is decided by the diameter/thickness ratio of grain. The grain size is smaller when B is the cosolvent than that of A, which enhances the value of Hu correspondingly. With the increase of pre-sintering temperature, when B is the cosolvent the grain growth is not obvious and the grain size is lower than the critical size of single-domain, which leads that the grains appear as hexagonal flake. But a remarkable grain growth was observed when B was replaced by A and some grain sizes exceed the critical size of single-domain, which makes the grain presenting as hexagonal bulk.2. La-Co partly vicarious M-type magnetic ferrites powders were prepared by solid-state reaction method. The experimental results show:the increase of grain size and diameter/thickness ratio can be partly suppressed by adding the iron contents of La-Co partly vicarious SrM magnetic powders. The value of HcJ increases gradually with the increase of iron contents at same pre-sintering temperature. In the experiment that the contents of Ca is changed in SrM magnetic powders partly replaced by Ca-La-Co, the grain size will be gradually enlarged with the increase of Ca contents, which results in the decrease of HcJ. When a small quantity of Ba is added in the Ca-La-Co M-type magnetic powders, the grain growth will be suppressed and the diameter/thickness ratio will be reduced, leading to the improvement of HcJ.3.By using improved ceramic technique, the sintered permanent magnetic ferrites of pure SrM, SrM partly replaced by La-Co, SrM partly replaced by Ca-La-Co, and Ca-La-Co M-type were prepared, respectively. The typical results are:SrM:Br=3.56 kGs, HcJ=2.63 kOe; La-Co-SrM:Br=4.09 kGs, HcJ=3.97 kOe; Ca-La-Co-SrM:Br=3.90 kGs, HcJ=5.18 kOe; Ca-La-Co M-type:B1=4.01 kGs, Hcj=4.69 kOe. It can be seen that the value of HcJ of SrM can be enhanced obviously by replacing with La-Co, the HcJ value of Ca-La-Co M-type magnetic ferrites is larger than that of La-Co-SrM, and the value of HcJ of Ca-La-Co SrM magnetic ferrites can reach 5.18 Oe. The Br value of M-type magnetic ferrites will be enhanced by partly replaced with different ions, however, the overall level of Br is not high enough, which is mainly because the size distribution is not uniform after the secondary fine grinding and the degree of orientation can’t be improved effectively.4. The results by modulating the preparation technology of sintered permanent magnetic ferrites indicate that the Br value of magnetic ferrites adding Co in pre-sintering process is larger than that in second ball-milling process, but the coercivity of CoFe204 is lower composited by adding Co in pre-sintering process, resulting in the decrease of HcJ value and the appearance of drop-offs in the demagnetizing curve of J. The grain sizes reduce by extending the time of second ball-milling process, and the HcJ value is enhanced. However, the size distribution will be not uniform since the increase of tiny particles, which can reduce the value of Br. The above situation can be improved by extending the fine grinding time, and the effect of magnetic orientation can improve correspondingly, which can enhance the Ha, and keep the Br from reducing.5. Using the finer Fe2O3 as raw materials, the uniform pre-sintering powders with smaller grain size can be obtained by solid-state reaction method. The SrM permanent magnetic ferrites partly replaced by La-Co own both enhanced Br and HcJ via using above uniform pre-sintering powers. Besides, the time of second ball-milling process can be reduced effectively, and the efficiency is improved. The typical magnetic parameters are Br=4.28 kGs, HcJ-4.30 kOe, (BH)max=4.32 MGOe.