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Ba-Ferrite 단결정의 자기적 특성에 관한 뫼스바우어 분광학적 연구
서정철,지성훈,홍양기,Sur, J.C.,Gee, S.H.,Hong, Y.K. 한국자기학회 2007 韓國磁氣學會誌 Vol.17 No.2
Ba-Ferrite single crystals were prepared and characterized by X-ray, SEM and Mossbauer spectroscopy. The single crystal layers was cut in the c-axis and radiated to the surface by ${\gamma}-rays$ for Mossbauer spectroscopy. We found out that the spin states in Fe atoms were parallel to the ${\gamma}-rays$ direction. The temperature dependence of the hyperfine field is almost similar to that of powder samples. The crystal structure is a Magnetoplumbite without any other phases and the lattice parameters are found out with $a_0=5.892{\AA},\;b_0=5.892{\AA},\;c_0=23.198{\AA}$. $M\"{o}ssbauer$ spectrum in single crystal have 5 sets off absorption lines in each Fe site when the ${\gamma}-rays$ have the same radiation direction with the c-axis in the crystal, which mean that the whole crystal bulk formed only one crystal and same spin direction. The hysteresis curve shows the saturation moment and coercive force of 70.71 emu/g and 320 Oe respectively. Ba-ferrite 단결정을 제조하여 자기적 성질을 Mossbauer 분광법으로 연구하였다. 단결정 시료를 c-축 방향으로 얇게 절단하고 그 면에 감마선을 조사한 결과 결정 전체에 걸쳐 Fe 이온의 스핀 방향이 c-축과 일치함을 확인하였다. 온도에 따른 초미세자기장의 감소 추세는 입자상태와 거의 비슷하였으며 결정 내 Fe원자의 이온 상태 역시 일치하였다. 결정구조는 Magnetoplumbite로서 결정상수는 $a_0=5.892{\AA},\;b_0=5.892{\AA},\;c_0=23.198{\AA}$로 정되었으며 그 외의 다른 상은 존재하지 않는 것으로 나타났다. $M\"{o}ssbauer$ spectrum은 결정 내에 존재하는 Fe의 자리에 따라 5의 각각의 다른 subspectrum이 존재하였는데 감마선의 방향이 c-축과 일치하여 모든 자리에서 4개의 공명흡수선 만이 존재하였다. 따라서 결정의 형태는 전체적으로 단일상으로 형성되었음을 확인하였고 여분의 ${\alpha}-Fe_2O_3$ 등은 존재하지 않음을 명확히 하였다. 자기이력곡선을 통하여 실온상태에서 포화자기모멘트는 70.71 emu/g, 보자력이 320 Oe의 값으로 측정되었다.
Ba-Ferrite 단결정의 자기적 및 열적 현상에 관한 미시적 연구
서정철(J. C. Sur),최정완(J. W. Choi) 한국자기학회 2009 韓國磁氣學會誌 Vol.19 No.4
Ba-Ferrite single crystals were prepared and the magnetic and thermal properties were characterized by Mossbauer spectroscopy. The single crystal layer was cut in the c-axis and radiated to the surface by γ-rays for Mossbauer spectroscopy. We found out that the spin states in Fe ions were parallel to the γ-rays direction and the whole crystal bulk formed only one crystal with the same spin direction . Mossbauer spectra in single crystal have only 4 sets of 4 absorption lines in each Fe site when the γ-rays have the same radiation direction with the c-axis in the crystal, and there was no 2b-site spectrum. The zero absorption of 2b-site means that there was a fast diffusion motion in a double-well atomic potential at room temperature, in which bipyramidal Fe ions have the two minima at each side mirror plane.
Mossbauer Study of Co0.3Fe0.7Cr₂S₄
김철성(C. S. Kim),하민용(M. Y. Ha),이운화(W. H. Lee),윤성로(S. R. Yoon),서정철(J. C. Sur) 한국자기학회 1992 韓國磁氣學會誌 Vol.2 No.3
Co_(0.3)Fe_(0.7)Cr₂S₄ has been studied by Mossbauer spectroscopy and X-ray diffraction, The crystal structure is found to be a cubic spinel with the lattice parameter α。=9.967 Å. Mossbauer spectra have been collected over the temperature range 12 K ~ 300 K. The absence of quadrupole splitting above the Neel temperature T_N indicates that iron ions occupy only the tetrahedral (A) sites, The isomer shift indicates that the charge state of a Fe ion is ferrous in character. It is notable that as the temperature decreases below T_N=184 K, both quadrupole splitting and asymmetrical line broadening appear and increase with decreasing temperature, suggesting the appearence of a dynamic Jahn-Teller distortion. The magnetic hyperfine field and quadrupole splitting at 12 K are found to be 193 kOe and 1.10 ㎜/s, respectively, Debye temperature is found to be 218 K.
In 이온을 첨가한 EuFeO₃의 결정구조 및 자기적 성질
김정기(J. G. Kim),서정철(J. C. Sur),한은주(E. J. Han) 한국자기학회 1994 韓國磁氣學會誌 Vol.4 No.4
The crystallograpic and magnetic properties of Eu(Fe_(1-x)In_x)O₃ (x = 0, 0.03과 0.05) have been studied by the methods of X-ray diffraction, Mossbauer spectroscopy, and magnetic hysteresis measurement at room temperature. The X-ray results show that the samples have a crystal structure of orthorhombic and unit cell volume of the crystal with the exception of the sample of x = 0 increases as increasing the In concentration. In the analysis assuming two sets of six-line of Mossbauer spectra, it is found that the magnetic hyperfine field in each of sets decreases increasing x. The linewidth of the absorption lines for the samples increased as increasing x. This implies that the data involve a sum of several hyperfine patterns which have intensity being proportional to nPz(X), the probability of an environment with z such Fe neighbors. The magnetic hysteresis curves show decrease of Ms and increase of Hc of the samples with increasing x.
김정기(J. G. Kim),서정철(J. C. Sur),한은주(E. J. Han) 한국자기학회 1993 韓國磁氣學會誌 Vol.3 No.2
The crystallographic properties of the polycrystalline materials Fe_(1+x)Eu_(l-x)O₃(x = -0.06, 0.0, 0.1, 0.2, 0.3, 0.4) have been studied by the methods of X-ray diffraction and Mossbauer spectroscopy. The results showed that the samples with the composition range of 0.2 ≤ x ≤ 0.3 had the garnet crystal phase, while those with -0.06 ≤ x ≤ 0.0 had the orthoferrite phase. However, with the tendency for the orthoferrite phase to convert into the trigonal phase via garnet phase as increasing the composition x, the orthoferrite-garnet and garnet-trigonal phase coexisted dominantly in the range of 0.0 < x < 0.2 and 0.4 ≤ x, respectively. The analyzed results of Mossbauer spectrum indicated existence of some vacancies in the d-site of garnet phase, which can be related to the change of intensity in X-ray diffraction patterns.
김정기(J. G. Kim),한경훈(K. H. Han),서정철(J. C. Sur) 한국자기학회 1999 韓國磁氣學會誌 Vol.9 No.4
The crystallographic and magnetic properties of the system of Fe_(1-x)Co_x (x=0.2 and 0.4) prepared by microwave arc-melting with the maximum power of 3.5 ㎾ and a iron-foil with thickness of 25 ㎛ have been studied by the methods of X-ray diffraction and the measurement of the magnetic hysteresis using the vibrating sample magnetometer at room temperature. The samples were prepared in three different ways: First, pellet form pressed under the pressure of 9,000 N/㎠. Second, thin sheet cold rolled. Third, thin sheet treated with the temperature of 900℃. The X-ray diffraction pattern of the sample prepared by the first method shows that the crystal structure of the sample is bcc as same as that of Fe with a good uniformity. The iron-foil has the coercivity of 43 Oe and the initial slope of magnetization of 0.328 emu/gOe. The coercivity and magnetization of the sample prepared by the second method increased as the Co content increased. But the initial slop of the magnetization decreased as the Co content increased. This means that the displacement of domain wall is suppressed by the increase of coercivity as the Co content increased. The saturation magnetization of the samples made by the third method increased. On the other hand, the coercivity of these samples decreased. The increase of saturation magnetization of the samples seems to be related to the changes in X-ray intensity after heat treatment. Also some magnetic parameters of the samples were calculated by using a simple model and compared with other values.
다결정(Fe, In, Eu)₂O₃ 계의 자기적 성질에 관한 연구
김정기(J. G. Kim),서정철(J. C. Sur),한은주(E. J. Han),홍양기(Y. K. Hong) 한국자기학회 1991 韓國磁氣學會誌 Vol.1 No.1
The magnetic properties of the polycrystalline (Fe₂O₃)_(1-x-y)(In₂O₃)_x(Eu₂O₃)_y (x=0.01, y=0.02 and x=0.02, y=0.03) have been studied by the methods of X-ray diffraction, Mossbauer effect, and magnetic hysteresis measurement. The X-ray diffraction patterns show that the samples have a same crystal structure as α-Fe₂O₃. From the analysis of the temperature dependence of the quadrupole splitting and average half-width, it is found that the Morin transition occurs in the sample of x=0.01 and y=0.02 and the spin angle defined as the angle between the [111] crystal axis and antiferromagnetic vector, changes from about 35° to the (111) plane as increasing the temperature in the sample of x=0.02 and y=0.03. The temperature dependence of magnetic hyperfine field is analyzed by using the spin-wave theory. The isomer shift values at room temperature are found to be given by about 0.35㎜/s for the samples which means that the Fe ions belong to 3+ion. The temperature dependence of isomer shift was analyzed by using the Debye model.