| Hexagonal ferrites are widely used in microwave devices, magneto-optic systems and high density magnetic recording medium because of a series of advantages such as low price of raw materials, excellent chemical stability and large magnetocrystalline anisotropy. In recent years, many interests have been focused on the high performance strontium ferrites in order to meet the requirements of the portability and energy saving of automobile, communications, office supplies and consumer products.In this dissertation, Based on the Y30H-2 pre-sintered powders, La-Co and La-Zn substituted M-Type high performance strontium ferrites were prepared by common ceramic processing. The micro-structures and magnetic properties of the samples were systematically investigated by X-ray diffraction(XRD), scanning electron microscope(SEM) with EDS and MATS-2010H magnetometer. The effect of CaCO3, SiO2 and Al2O3 additives with different particle sizes on the micro-structures and magnetic properties of strontium ferrites have been systematically studied.The results of XRD and SEM analysis showed that La3+ and Co2+ have been completely doped into strontium ferrite phase for Sr1-xLaxFe12-xCoxO19(x≤0.30) samples sintered at 1100℃1215℃. With the increase of La-Co content x, the remanence(Br) and coercivity(Hcj) of the samples increased at first, and then decreased. The maximum Br of doped samples sintered at 1170℃for x=0.12 only increased 2.28% compared to undoped samples, whereas the maximum Hcj of doped samples sintered at 1170℃for x=0.15 increased 24.29% compared to undoped samples. The results, thus, indicated that Hcj might be remarkably improved by La-Co substitution. The optimal magnetic properties in La-Co substituted samples were obtained as: Br=411.9mT, Hcb=291.3kA/m, Hcj=332.9kA/m, (BH)max=31.9kJ/m3 for the composition of x=0.15, sintered at 1170℃.The optimal formulae of additives including CaCO3, SiO2, H3BO3, SrCO3 were determined by orthogonal experiments. The samples of La-Zn substituted SrM were prepared according to the formula Sr1-xLaxFe12-xZnxO19 (x≤0.27). The results of XRD and SEM analysis showed that La3+ and Zn2+ have also been completely doped into strontium ferrite phase sintered at 1155℃1215℃. With the increase of La-Zn content x, The Br of doped samples increased at first and then decreased, but the Hcj rapidly reduced at first and then decreased slowly when x≥0.12. The maximum Br of doped samples sintered at 1200℃for x=0.09 increased 2.27% compared to the undoped samples.The experimental results indicated that the Br of strontium ferrites could be effectively improved but Hcj could be remarkably reduced by La-Zn substitution. The optimal magnetic properties with Br=427.3mT, Hcb=184.0kA/m, Hcj=189.0kA/m and (BH)max=33.8kJ/m3 were obtained in La-Zn substituted Sr0.91La0.09Fe11.91Zn0.09O19 ferrites sintered at 1200℃.The additives of CaCO3, SiO2, Al2O3 with different particle sizes have different effects on the magnetic properties of Sr-ferrites. The studies showed that the nano-additives have more significant effects on the magnetic properties of strontium ferrite compared with microadditives.
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