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치환형 Sr - Ba 육방 페라이트들의 자기적 성질에 수소환원이 미치는 효과에 관한 Mossbauer 분광학적 연구
박재윤(J. Y. Park),권명희(M. H. Kwon),이재광(J. G. Lee) 한국자기학회 1999 韓國磁氣學會誌 Vol.9 No.1
Sr substituted materials for some barium in M-type barium ferrite powder and Co-Ti substituted Sr-Ba hexagonal ferrite powder were prepared by citrate sol-gel method and 2 MOE sol-gel method. These hexaferrite particles were reduced for 1hr in the hydrogen gas. The reduction temperatures were varied in the range of 250 ℃ to 500 ℃. X-ray diffraction patterns were measured using diffractometer with Cu Kα radiation. Mossbauer absorption spectra were measured with a constant acceleration spectrometer. We have focused on studying the origin of increasing Ms by Mossbauer spectroscopy. Ferrite particles which were sintered at 1050 ℃ were found to be typical magnetoplumbite structure and single phase. XRD patterns with varying the reduction temperatures in Sr_(0.5)Ba_(0.5)Fe_(10)O_(19) indicates ferrites particles become composite hexaferrites containing α-Fe at Tred. = 350 ℃. On the otherhand, it was found that Co²+ ions and Ti⁴+ ions in Sr_(0.7)Ba_(0.3)Fe_(10)CoTiO_(19) prevent from changing Fe³+ ions to α-Fe during the H₂ reduction. Comparing Mossbauer results with XRD results, we have determined most of α-Fe are reduced from 4fvi sites and 12k sites of Fe³+ ions. These α-Fe phase bring the induced anisotropy and increase saturation magnetization Ms.
이재광,권태송,박기택,김철구,조육 연세대학교 자연과학연구소 1984 學術論文集 Vol.13 No.-
Thomas-Fermi 근사와 Resta의 모델을 사용하면 r-공간의 반도체 유전함수를 계산할 수 있다. 그러나 절대온도 OK에서는 반도체에 Resta의 모델을 적용하는 것이 개념상 곤란하므로, Lannoo와 Allan의 모델과 TF방정식을 이용하여 Resta모델의 문제점을 해결한 간단하고 해석적인 유전함수를 구하였다. 이때 구한 유전함수는 Resta의 결과에 비하여 정밀한 수치계산 값과 더 잘 일치하였다. r-space dielectric function can be obtained by using the Thomas-Fermi approximation and the Resta’s model. However, the Resta’s model encounters a conceptual difficulty when applied to semiconductors at the absolute zero temperature. By applying the Lannoo and Allan model to the Thomas-Fermi equation, we obtained a simple and analytic dielectric constant which is at the same time free of the difficulties encounted in the Resta’s model. The obtained dielectric function gives a better agreement with a more elaborate numerical calculation than the Resta’s result.