| M-type magnetic magnetoplumbite ferrite Ba Fe12O19?Ba M?and Sr Fe12O19?Sr M?are widely used in industry due to its high coercivity,fine chemical stability and good cost-performance.Currently,the preparation and the modification of its magnetic properties through substitution are still extensively studied.In this thesis,Ba M ferrite powders were synthesized by a hydrothermal method,and the effects of Ba/Fe ratio,OH-/NO3-ratio,hydrothermal temperature and acid washing on their phase composition,microstructures and magnetic properties were studied.Moreover,the Sr M ferrite powders were prepared by a ceramic method,and the effects of Sr/Fe ratio,sintering temperature and the substitution of rare earth Ce and its co-substitution on their phase composition,microstructures and magnetic properties were also studied.For the BaM ferrite synthesized by the hydrothermal method,it is found that the single-phase Ba M ferrite can be obtained under the conditions of Ba/Fe=1:9,OH-/NO3-=3:1 and a hydrothermal temperature of 220oC×6 h.The magnetic properties decrease with the decrease of Ba/Fe,accompanying with the decrease of average grain size.In addition,the impurity Ba CO3and Fe2O3 in the specimens also reduce the magnetic properties,while the acid washing can eliminate the impurities and consequently improve their saturation magnetization to a certain degree.For the SrM ferrite synthesized via the ceramic method,the single-phase Sr M ferrites without substitution can be obtained when the Sr/Fe ratio is 1:9.6 and sintering temperature is1200oC×3 h.It was also found that compared with the Sr M ferrite without substitution,suitable Ce substitution for Fe helps to enhance the saturation magnetization and coercivity;while the substitution of Ce for Sr reduces the coercivity greatly,though accompanying a considerable increase of saturation magnetization.In addition,the saturation magnetization increases for the specimens with Ce-Co co-substitution for Sr-Fe,while the coercivity also decreases greatly. |
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