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Hexaferrite 쉬트자석의 개발과 자기적 성질에 관한 연구
김철성(Chul Sung Kim),박승일(Seung IeI Park),오영제(Young Jei Oh) 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.4
In order to study the effect of additives SiO₂ on the magnetic properties of hexaferrite sheet magnet, we used X-ray diffractometer, Mossbauer spectrometer, and VSM magnetometer. We have prepared Ba_(0.25)Sr_(0.75)Fe₁₂O_(19) green sheets by the Dr. Blade method. Most of samples have a magnetoplumbite crystal structure of typical M-type hexaferrite. The lattice parameters are found not to be affected by the addition of SiO₂. α-Fe₂O₃ phase develops above SiO₂ 2.0 wt. %. Isomer shifts indicate that the valence of Fe ions is trivalent. Curie temperatures decrease slightly with increasing SiO₂ concentrations. It means that the Si⁴+ subsitution for 12k-site Fe³+ has an effect on the superexchange interactions Fe-O-Fe, which change the distance and the angle between cations and anions. It was suggested that α-Fe₂O₃ phase results from the excessive Fe produced by subsituting Si⁴+ for Fe³+. Based upon the results of Ba_(0.25)Sr_(0.75)Fe₁₂O_(19) added with SiO₂, we concluded that Hc, Ms and Mr depend more strongly on the microstructure characteristics than on the cation substitution.