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Chromite 물질의 자기상호작용에 관한 뫼스바우어 분광연구
최강룡,김철성,Choi, Kang-Ryong,Kim, Chul-Sung 한국자기학회 2007 韓國磁氣學會誌 Vol.17 No.1
최근 geometrical frustration 현상 및 멀티페로익 효과가 Cr 이온의 나선 스핀 구조에 기인하는 것으로 해석되고 있다. 이에 본 연구에서는 Cr 이온 자리에 Fe을 치환하여 $CoCrFeO_4$를 제조하였고, $M\"{o}ssbauer$ 분광법에 의해 자기적 미세 구조의 상관관계를 연구하였다. 졸겔법을 이용하여 Fd3m의 cubic 스피넬 구조를 갖는 $CoCr_2O_4,\;CoCrFeO_4$ 단일상을 합성하였고, Rietveld 법에 의한 분석결과 격자상수는 $a_0=8.340$에서 $8.377{\AA}$로 증가 하였으며, Cr, Fe 이온은 모두 팔면체 구조에 위치하는 것으로 분석되었다. 자기 상전이 온도는 $T_N=97K$에서 320 K로 증가하였으며, 상호작용의 변화에 따라서 field cooled 온도에 따른 자화 곡선의 변화를 관측하였다. $M\"{o}ssbauer$ 스펙트럼 분석결과 4.2 K에서 공명흡수선에 대한 초미세자기장($H_{hf}$) 값은 각각 507, 492 kOe 정도로 나타났으며, 이성질체 이동치($\delta$)는 0.33, 0.34 mm/s 정도로 Fe 이온상태가 둘 다 +3 가의 이온상태임을 알 수 있었다. [ $ZnCr_2O_4$ ] shows geometrically frustrated magnet. Recently, $CoCr_2O_4$ has been investigated for multiferroic property and dielectric anomalies by spin-current model. Polycrystalline $CoCr_2O_4$ and $CoCrFeO_4$ compounds was prepared by wet-chemical process. Crystallographic and magnetic properties of $CoCr_2O_4$ and $CoCrFeO_4$ were investigate by using the x-ray diffractometer(XRD), vibrating sample magnetometer(VSM), superconducting quantum interference device magnetometer(SQUID), and $M\"{o}ssbauer$ spectroscopy. The crystal structure was found to be single-phase cubic spinel with space group of Fd3m. The lattice constants of $CoCr_2O_4$ and $CoCrFeO_4$ $a_0$ were determined to be 8.340 and 8.377 ${\AA}$, respectively. The ferrimagnetic transition temperature for the both samples were observed at 97 K and 320 K. The $M\"{o}ssbauer$ absorption spectra at 4.2 K show that the well developed two sextets are superposed with small difference of hyperfine field($H_{hf1}=507\;and\;H_{hf2}=492\;kOe$). Isomer shift values($\delta$) of the two sextets are found to be 0.33 and 0.34 mm/s relative to the Fe metal, respectively, which are consistent with the high spin $Fe^{3+}$ charge state.
Co<SUB>0.9</SUB>Zn<SUB>0.1</SUB>Cr<SUB>1.98</SUB>⁵⁷Fe<SUB>0.02</SUB>O₄ 물질의 초미세자기장 연구
최강룡(Kang Ryong Choi),김삼진(Sam Jin Kim),김철성(Chul Sung Kim) 한국자기학회 2008 韓國磁氣學會誌 Vol.18 No.1
AB₂X₄ (A, B = Transition Metal, X = O, S, Se) are cubic spinel normal ferrimagnets, in which M ions occupy the tetrahedral sites and Cr ions occupy the octahedral sites. Recently, they have been investigated for behaviour of B site ions and A-B interaction. Polycrystalline [Co<SUB>0.9</SUB>Zn<SUB>0.1</SUB>]<SUB>A</SUB>[Cr<SUB>1.98</SUB>??Fe<SUB>0.02</SUB>]<SUB>B</SUB>O₄ compound was prepared by wet-chemical process. The ferrimagnetic transition was observed around 90 K. Mossbauer absorption spectra at 4.2 K show that the well-developed two sextets are superposed with small difference in hyperfine fields (H<SUB>hf</SUB>). The hyperfine fields of Co<SUB>0.9</SUB>Zn<SUB>0.1</SUB>Cr<SUB>1.98</SUB>??Fe<SUB>0.02</SUB>O₄ and Co<SUB>0.9</SUB>Zn<SUB>0.1</SUB>Cr<SUB>1.98</SUB>??Fe<SUB>0.02</SUB>O₄ were determined to be 488, 478 kOe and 486, 468 kOe, respectively. We notice that the one of the magnetic hyperfine field values changes with Zn ion substitution. These results suggest the incommensurate states and spin-reorientation temperature (T<SUB>S</SUB>= 18 K) changes with Zn ions substitution below spin-reorientation temperature (T<SUB>S</SUB>= 28 K) of Co<SUB>0.9</SUB>Zn<SUB>0.1</SUB>Cr<SUB>1.98</SUB>??Fe<SUB>0.02</SUB>O₄.
Fe이 치환된 LaBaMnO계 산화물의 중성자 회절 및 Mossbauer 분광학연구
최강룡(Kang Ryong Choi),김삼진(Sam Jin Kim),심인보(In-Bo Shim),김철성(Chul Sung Kim) 한국자기학회 2004 韓國磁氣學會誌 Vol.14 No.1
The iron doped colossal magnetoresistance materials with La-Ba-Mn-O perovskites structure have been synthesized by chemical reaction of sol-gel methods. Their crystallographic and magnetic properties have been studied with x-ray diffraction, VSM, RBS, Mossbauer spectroscopy, and magnetoresistance measurements. The crystal structure of the La_(0.67)Ba_(0.33)Mn_(0.09)Fe_(0.01)O₃ at room temperature was determined to be orthorhombic of Pnma. The lattice parameters α_0 and c_0 increased gradually, but b_0 deceased with increase of iron substitution. The magnetization and coercivity deceased, also the Curie temperature decreased from 360 K as x increased from 0.00 to 0.05. Magnetoresistence measurements were carried out, and the maximum MR (△ρ/ρ(0)) was observed at 281 K, about 9.5 % in 10 kOe. The temperature of maximum resistance (R_(MAX)) decreased with increasing substitution of Fe ions and a semiconductor-metal transition temperature (T_(SC-M)) decreased too. This phenomena show that ferromagnetic transition temperature decreased by substituting Fe for Mn ions, it decreases double exchange interaction. This result accords with magnetic structure of neutron diffraction. Mossbauer spectra of La_(0.67)Ba_(0.33)Mn_(0.99)(57)^Fe_(0.01)O₃ were taken at various temperatures ranging from 15 to 350 K. With lowering temperature of the sample, two magnetic phases were increased and finally it showed the two sharp sextets of spectra at 15 K. The isomer shift at all temperature range is about 0.3 ㎜/s relative to Fe metal, which means that both Fe ions are Fe³+ states.
PZT / LSMO / Pt에 대한 펄스레이저 및 졸겔법에 의한 증착연구
최강룡(Kang Ryong Choi),심인보(In-Bo Shim),김철성(Chul Sung Kim) 한국자기학회 2005 韓國磁氣學會誌 Vol.15 No.1
This work is to present each properties and the interfacial characterization between PZT layer and LSMO layer of PZT/LSMO/Pt. LSMO thin film grown by KrF (248 ㎚) excimer lasers are used in pulsed laser deposition(PLD). PZT composites thin films were deposited by spin coating using a commercial resist spinner. LSMO thin film by deposition oxygen pressure 125 mtorr have rhombohedral structure on Pt(111) substrate. The PZT/LSMO/Pt pre-orientate to [111] direction. The final thin films were shown that magnetic and electric property was typical value, respective. We report that the lattice between the PZT/LSMO thin film and the substrate plays a very important role and may control to another effects.