| Due to its high magnetic properties, excellent corrosion resistance, low price and ease of industrial production, etc., srontium hexaferrite(Sr Fe12O19) has been a very important permanent magnet materials. However, with the miniaturization trend and expanding application of magnetic devices, higher requirements are put forward about M type srontium hexaferrite. Although China has already been the largest producer of hard ferrite in the world, most of the products are mainly focused on the low-end market, and the output and market share of high-performance products are far lower than Japan, Europe and the United States and other developed countries. Therefore, the study of high-performance permanent magnet strontium ferrite is not only the urgent needs of the market, but also of great significance to improve the technical level of permanent ferrite.In this thesis, based on the trace amount of Al ions and the usage of pre-sintering material, different kinds of ion-doped(Al, Al-La, Al-Co, Al-La-Co, Al-Zn, Al-Ti-doped) M type Sr-hexaferrite were successfully synthesized by ceramic processing. Besides, the influence of sintering process on the ions doped Sr-hexaferrite were also investigated. Then, the crystal structure, microstructure and magnetic properties of each doped samples were Systematically studied by X-ray diffraction(XRD), field emission scanning electron microscopy(SEM) and comprehensive Physical property measurement System(PPMS). The main results were presented as follows:(1) XRD and SEM results indicated that the optimum sintering process of Sr Fe11.8Al0.2O19 sample was sintered at 1250 ℃ for 90 min. The Sr Fe11.8Al0.2O19 samples sintered in the range of 1190 ℃ to 1290 ℃ were all single phase. VSM results showed that with the increase of sintering temperature the Hc of Al-doped samples increased while the Br and(BH)max reached a peak at about 1250 ℃ and then decreased rapidly when the temperature continued to rise. The optimal magnetic properties was obtained at 1250 ℃ for 90 min with Hc = 4919 Oe, Br = 384 m T, and(BH)max = 28.1 k J/m3.(2) Based on the XRD results, the Sr Fe12-x Alx O19 samples with different Al content were all single phase after sintering at 1250 ℃ for 90 min. SEM results showed that particles were evenly distributed and no abnormal grain growth were found. However, with the increase of sintering temperature the grain boundaries of each sintered particles have a tendency of integration. VSM analysis showed that with the increase of Al ions the Hc of the samples increased linearly while the Br and(BH)max gradually decreased. Compared with the un-doped samples, the Br of Sr Fe11.3Al0.7O19 samples decreases by 21.41%, but Hc increased by 47.92%.(3) The optimal sintering temperature of Sr0.85La0.15Fe11.8Al0.2O19 sample was 1230 ℃, suggesting that La ions have an effect on the sintering characteristics of strontium ferrite. VSM results showed that the Br and Hc of Sr1-y Lay Fe12-x Alx O19 samples increased at first and then decreased with the increase of La content(y). For x = 0.2, 0.3, 0.4, the largest growth of Br were 2.24%, 1.61% and 3.13% respectively, and the largest growth of Hc were 9.69%, 4.32% and 5.71% respectively. The variation tendency of Br for Sr Fe12-x-y Alx Coy O19 samples was similared to that of Al-La doped, showing a decreasing trend after the first increase. For x = 0.2, 0.3, 0.4, the largest growth of Br were 0.95%, 2.00% and 2.30% respectively. Different from the trends of Br, the Hc of Sr Fe12-x-y Alx Coy O19 samples decreased linearly as Co content increased. The optimal magnetic properties were obtained by Sr0.9La0.10Fe11.7Al0.2Co0.10O19 sample with Br = 390 m T and Hc = 5284 Oe, in which Br and Hc increased 1.65% and 9.33% respectively compared to those un-doped samples.(4) VSM results showed that the Br and Hc of Sr Fe11.8Al0.2O19 samples contained Zn or Ti ions both increased at first and then decreased as the added ions increased linearly. For the former, the peak appeared approximately at y = 0.10 with Br = 395 m T and Hc = 4033 Oe; for the latter, it came to around y = 0.05 with Br = 387 m T, Hc = 4619 Oe. It can be seen that the effect of Zn-doped on the Br of Al-doped Sr-hexaferrite samples was better than that of Ti ions. |
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