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Cu0.1Fe0.9Cr₂S₄의 결정학적 및 자기적 성질에 관한 연구
손배순(Bae Soon Son),김삼진(Sam Jin Kim),김철성(Chul Sung Kim) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.1
Cu_(0.1)Fe_(0.9)Cr₂S₄ has been studied with Mossbauer spectroscopy, x-ray diffraction, vibrating sample magnetometer (VSM), and magnetoresistance (MR) measurement. The crystal structure was determined to be a cubic spinel with lattice parameter α_0 = 9.988 Å. The MR measurements show a semiconductor behavior below 110 K and metal behaved above 100 K. The temperature dependence of magnetization of Cu_(0.1)Fe_(0.9)Cr₂S₄ was reported. In addition to a large irreversibility between the zero-field-cooling (ZFC) and the field-cooling (FC) magnetization at applied field H=100 Oe, a cusp-like anomaly was observed in both the FC and ZFC curves. It shifted toward the lower temperature region with increasing magnetic field, and then showed convex type maximum at 110 K, under the applied field of 5 kOe. The Mossbauer spectra were measured from 15 K to room temperature. The asymmetric line broadening was observed for the sample Cu_(0.1)Fe_(0.9)Cr₂S₄, and it was considered to be dynamic Jahn-Teller relaxation. The charge state of Fe ions was ferrous in character. The unusual reduction of magnetic hyperfine field below 110 K was interpreted in terms of cancellation effect between the mutually opposite orbital current field (H_L) and Fermi contact field (H_C).
뫼스바우어 효과를 통한 FeIn₂S₄에서의 Fe2+ 초미세 상호 작용 연구
손배순(Bae Soon Son),김삼진(Sam Jin Kim),김철성(Chul Sung Kim) 한국자기학회 2007 韓國磁氣學會誌 Vol.17 No.1
FeIn₂S₄를 제조하여 뫼스바우어 분광기, X-선 회절기, SQUID 자화율 측정기를 이용하여 결정학적 및 자기적 특성을 연구하였다. 결정구조는 역스피넬 구조로 In 이온은 각각 사면체 자리(A site)와 팔면체 자리(B site)에 동시에 존재하는데 비하여, Fe 이온은 팔면체 자리에만 존재하였다. Curie-Weiss 역자화율에 따른 유효자기모멘트는 5.09 µB였으며, 닐온도(Néel temperature)는 13 K였다. 이와 같이 낮은 닐온도는 팔면체 자리의 Fe2+(B)-S2--Fe2+(B)의 초미세 상호작용이 약하기 때문인 것으로 설명되어진다. 전기사중극자 상호작용의 온도 의존성은 z-축에 따른 결정장 이론으로 설명되어진다. The FeIn₂S₄ exhibits an inverse spinel which Fe ions are occupied to the octahedral (B) site, while In ions are occupied to both the tetrahedral (A) and the octahedral (B) site. The Néel temperature (TN) is determined to be 13 K. The effective moment of FeIn2S4 is found to be 5.094 µB from the fit of Curie-Weiss inverse susceptibility for the temperature range over TN, implying angular momentum contribution. The angular momentum contribution is shown in Mössbauer spectra for the antiferromagnetic ordering region (T≤ 13 K), too. A weak Fe2+(B)-S2--Fe2+(B) interaction is responsible for a low Néel temperature (TN) in FeIn₂S₄ system. The temperature dependence of electric quadrupole interaction is explained by z-axial crystalline field energy.
비자성 이온 Ga, In이 치환된 유화물 스피넬의 뫼스바우어 분광학 연구
손배순(Bae Soon Son),김삼진(Sam Jin Kim),김철성(Chul Sung Kim) 한국자기학회 2006 韓國磁氣學會誌 Vol.16 No.1
The sulphur spinel FeCr₂-xMxS₄ (M=Ga, In) have been studied with Mossbauer spectroscopy, x-ray diffraction (XRD), and vibrating sample magnetometer. The XRD patterns for samples FeCr₂-xMxS₄ (M=Ga, In; x=0.1, 0.3) reveal a single phase, which the Ga and In ions are partially occupied to the tetrahedral (A) site. The Neel temperature for the Ga substituted samples increases from 180 to 188 K, with increase from x=0.1 to 0.3. While, it decreases from 173 to 160 K, for the In substituted samples of the x=0.1 and 0.3, respectively. The Mossbauer spectra were collected from 4.2 K to room temperature. We have analyzed the Mossbauer spectra using eight Lorentzian lines fitting method for the FeCr₂-xInxS₄ (x=0.1) at 4.2 K, yielding the following results; Hhf=146.0 kOe, △E_Q=1.88 ㎜/s, θ=36˚, φ=0˚, η=0.6, and R=1.9. The Ga ions enter into the both sites octahedral (B) and tetrahedral (A), simultaneously the same amounts of Fe ions migrate from the A to the B site, this result is an agreement with XRD results, too. The △EQ of the A and B site in Mossbauer spectra of the samples FeCr₂-xGaxS₄ (x=0.3) are 0.83 and 2.94 ㎜/s, respectively. While they are 0.56 and 2.36 ㎜/s for the FeCr₂-xInxS₄ (x=0.3). It is noticeable that the △E_Q for the Ga doped samples are larger than that of the corresponding In doped samples, in spite of the larger ionic radius for In ions. The bond lengths of Cr-S, for the Ga and In doped samples (x=0.3) are found to be 2.41 and 2.43 Å, respectively. We interpret that the larger covalence effect from the smaller bond length induces a large asymmetric charge distribution. Finally, it gives a large quadrupole interaction.