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김광주(Kwang Joo Kim),박종호(Jongho Park),김영욱(Young-Wook Kim) 한국자기학회 2018 韓國磁氣學會誌 Vol.28 No.1
Electrical resistivity measurements were performed on Fe-doped bulk silicon carbide specimens in the 5~300 K temperature range. The Si<SUB>1−x</SUB>Fe<SUB>x</SUB>C (x = 0.02, 0.03, 0.04) specimens have zincblende structure and exhibited diluted ferromagnetic properties. The electrical resistivities of the specimens were in the 10<SUP>0</SUP>~10¹ Ωcm range, decreasing with increasing temperature. The resistivity decreased with increasing Fe composition in the whole temperature range with more decrease as the temperature is lowered. The temperature characteristics of the resistivity were explained in terms of the polaronic hopping conduction model.
HMX 결정 표면에 NTO 결정의 응집현상에 관한 연구
김광주 ( Kwang Joo Kim ),서현호 ( Hyoun Ho Seo ) 한국공업화학회 2003 공업화학 Vol.14 No.2
Cyclotetramethylene tetraitramine (HMX) 결정 표면에 3-nitro-1,2,3-triazole-5-one(NTO) 결정을 응집시키는 연구가 회분식 냉각 결정화기에서 수행되었다. 용액에서 NTO 결정 생성에 대한 2차핵생성속도와 응집속도가 결정화 조업조건에 따라 on-line 분석되었다. 종을 이용한 2차핵생성에서 과포화가 응집을 형성시키는데 가장 중요한 인자였다. 종의 농도, 과포화도, 교반속도 등의 실험변수가 조사되었다. NTO의 2차 핵생성속도는 종의 농도가 증가함에 따라 증가하였다. HMX 결정표면에 응집 메커니즘은 othorkinetic 메커니즘과 일치하며 과포화의 3.2승 및 입자수의 2승에 의존하였다. 결과적으로 둔감화약과 민감화약의 응집은 화약의 민감성을 감소시키는 방법이 될 수 있다. Agglomeration between 3-nitro-1,2,4-triazole-5-one (NTO) and cyclotetramethylene tetranitramine (HMX) crystals was investigated in a batch cooling crystallizer. Secondary nucleation rate and agglomeration rate were measured directly during the crystallization. In the secondary nucleation using a seed, the supersaturation was the most important parameter in producing the agglomerated particles. The influences of concentration of HMX seeds, supersaturation, and agitation rate were discussed. The secondary nucleation of NTO crystals by seeding MMX crystals increased as the seed concentration increased. The agglomeration kinetic was correlated with the 3.2nd power of the solution supersaturation and the 2rf power of the number of the suspended particles. Othorkinetic mechanism was found in the agglomeration between NTO and HMX crystals. The agglomeration between insensitive and sensitive explosives may be a method to reduce the sensitivity of explosive compounds.
역스피넬 Fe₃O₄ 박막의 바나듐 도핑에 따르는 자기적 성질 변화
김광주(Kwang Joo Kim),최승리(Seung-Li Choi),박영란(Young Ran Park),박재윤(Jae Yun Park) 한국자기학회 2006 韓國磁氣學會誌 Vol.16 No.1
Effects of V substitution of Fe on the magnetic properties of Fe₃O₄ have been investigated by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), conversion electron Mossbauer spectroscopy (CEMS), and vibrating sample magnetometry (VSM) measurements on sol-gel-grown films. XRD data indicates that the VxFe₃-xO₄ films maintain cubic structure up to x=1.0 with little change of the lattice constant. Analyses on V 2p and Fe 2p levels of the XPS data indicate that V exist as V³+ mostly in the VxFe₃-xO₄ films with the density of V²+ ions increasing with increasing V content. Analyses on the CEMS data indicate that V³+ ions substitute tetrahedral Fe³+ sites mostly, while V²+ ions octahedral Fe²+ sites. Results of room-temperature VSM measurements on the films reveal that the saturation magnetization for the x=0.14 sample is larger than that of Fe₃O₄, while it becomes smaller than that of Fe₃O₄ for x≥0.5. The coercivity of the VxFe₃-xO₄ films is found to increase with x, attributed to the increase of anisotropy by the substitution of V²+(d³) ions into the octahedral sites.
졸-겔 방법을 이용하여 제작된 (Mn, Cr)xCo₁-xFe₂O₄ 박막의 구조적, 자기적 특성
김광주(Kwang Joo Kim),김희경(Hee Kyung Kim),박영란(Young Ran Park),박재윤(Jae Yun Park) 한국자기학회 2006 韓國磁氣學會誌 Vol.16 No.1
By substituting Mn or Cr for Co in inverse spinel CoFe₂O₄, MnxCo₁-xFe₂O₄ and CrxCo₁-xFe₂O₄ thin films were prepared by sol-gel method and their structural and magnetic properties were investigated. X-ray diffraction indicates that the cubic lattice constant increase for the Mn substitution while it hardly changes for the Cr substitution. Substitution of Mn²+ for octahedral Co²+ sites can explain the increase of lattice constant in MnxCo₁-xFe₂O₄. On the other hand, Substitution of Cr³+ for octahedral Co²+ and subsequent reduction of Fe³+ ion into Fe²+ are expected to happen. Mossbauer spectroscopy measurements on CrxCo₁-xFe₂O₄ indicate the existence of tetrahedral Fe²+ ions that are created through reduction of tetrahedral Fe³+ ions in order to compensate charge imbalance happened by Cr³+ substitution for octahedral Co²+ sites. On the other hand, no Fe²+ ions were detected by Mossbauer spectroscopy for MnxCo₁-xFe₂O₄. A migration of Fe³+ ions from octahedral to tetrahedral sites in MnxCo₁-xFe₂O₄ was detected by Mossbauer spectroscopy for x>0.47. Vibrating sample magnetometry measurements on the samples at room temperature revealed that the saturation magnetization increases by Mn and Cr substitution for certain range of x, qualitatively explainable in terms of the comparison of spin magnetic moment among the related transition-metal ions.