Preparation And Magnetic Properties Of SrFe₁₂O₁₉ Ferrite And Its Composites

M-type magnetoplumbite ferrite(SrFe12O19, SrM) is widely used because of its high coercivity(Hc) and fine chemical stability. Recently, the preparation and magnetic properties of SrM are still hot research topics.In this thesis, SrM ferrite was prepared via a sol-gel method using egg white protein as the binder of metal ions, and the effects of Sr/Fe ratio, sintering temperature(Ts) and usage of egg-white(Mew) on the phase formation, morphology and magnetic properties were studied. In addition, SrFe12O19/Fe-B(SrM/Fe-B) and SrFe12O19/CoFe2O4(SrM/CFO) composites were prepared by using the powders obtained via a hydrothermal or molten salt method, and their structure, magnetic properties and the conditions of realizing exchange coupling interaction are studied.For SrM ferrite prepared via a sol-gel method using egg white protein as the binder of metal ions, it is found that the single-phase SrM ferrite only can be obtained under the conditions of Sr/Fe = 1:8 and Ts between 1000°C and 1200°C. In addition, the Mew does not affect the phase composition of SrM ferrite but the crystallinity and Da decrease with the increase of Mew. The specimen with Mew=3 g exhibits the best Ms and Hc compared with the specimens with Mew=6 g and 9 g.For SrM/Fe-B composites sintered at different temperatures, it is found that the composites only consists of SrM and Fe-B powders for Ts = 500°C, while the ?-Fe is precipitated markedly for Ts = 600°C and 700°C, and the DSC shows that ?-Fe precipitates most severely when Ts is 690°C. It is also found that both Rm and Ts affect the saturation magnetization(Ms) and the Hc of composites. The smooth magnetic hysteresis loops suggest a typical single behavior in composite specimens and the existence of exchange coupling between SrM and Fe-B.For SrM/CFO and SrM/Fe-B composites obtained via a facile grinding way, the exchange coupling interaction between magnetically hard and soft phases is proved to exist according to the magnetic hysteresis loops and recoil loops. It can be found that different grinding time affects their Ms and Hc slightly. However, in our ground composite powders, the spacing of neighbor hard and soft magnetic grains is much larger than Lex and K of the soft phases is surely larger than 0, but our study proves that the conditions of realizing exchange coupling interaction may not be so stringent.