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방사광을 이용한 FeV<SUB>2</SUB>O<SUB>4</SUB> 스피넬 산화물의 덩치상태와 분말상태의 전자구조 차이 연구
황지훈(Jihoon Hwang),김대현(D. H. Kim),이은숙(Eunsook Lee),강정수(J.-S. Kang),김우철(W. C. Kim),김철성(C. S. Kim),한상욱(S. W. Han),홍순철(S. C. Hong),박병규(B.-G. Park),김재영(J.-Y. Kim) 한국자기학회 2011 韓國磁氣學會誌 Vol.21 No.6
The electronic structure of ferrimagnetic spinel oxide of FeV<SUB>2</SUB>O<SUB>4</SUB> has been investigated by employing soft x-ray absorption spectroscopy (XAS) and soft x-ray magnetic circular dichroism (XMCD). The Fe 2p and V 2p XAS spectra show that the valence states of Fe and V ions are ~Fe<sup>2.3+</sup> mixed-valent states and ~V3+ states, respectively. In Fe 2p XMCD spectra, finite XMCD signals are observed for divalent Fe<sup>2+</sup> states only, but not for Fe<sup>3+</sup> states. This finding indicates that the magnetic moments of Fe<sup>2+</sup> ions are ordered ferromagnetically but that those of Fe<SUP>3+</SUP> ions are cancelled, implying that Fe<sup>2+</sup> ions play an important role in determining magnetic properties of FeV<SUB>2</SUB>O<SUB>4</SUB>.
4각 딥드로잉 클래드판재 성형공정의 탄소성 유한요소해석
이민철(M. C. Lee),홍석무(S. M. Hong),황지훈(J. H. Hwang),심재원(J. W. Sim),이장호(J. H. Lee),정완진(W. J. Chung),전만수(M. S. Joun) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
In this paper, three-dimensional elastoplastic finite element approach to simulating a clad-metal sheet metal forming process is presented. The approach is based on a layered finite element mesh system with tetrahedral elements and a force imposing die to deal with blanking holder force. The predictions are compared with experiments, revealing that they are in a good agreement with each other.
연 X선 방사광 분광법을 이용한 TCr₂O₄(T = Fe, Co, Ni) 스피넬 산화물의 전자구조 연구
김현우(Hyun Woo Kim),황지훈(Jihoon Hwang),김대현(D. H. Kim),이은숙(Eunsook Lee),강정수(J.-S. Kang) 한국자기학회 2013 韓國磁氣學會誌 Vol.23 No.5
The electronic structures of TCr₂O₄ (T = Fe, Co, Ni) spinel oxides have been investigated by employing synchrotron radiation-based soft X ray absorption spectroscopy (XAS). The measured 2p XAS spectra of transition-metal ions reveal that Cr ions are trivalent (Cr<SUP>3+</SUP>), and all the T (T = Fe, Co, Ni) ions are divalent (Fe<SUP>2+</SUP>, Co<SUP>2+</SUP>, Ni<SUP>2+</SUP>). It is also found that most of T (T = Fe, Co, Ni) ions occupy the A sites under the tetrahedral symmetry, while Cr ions occupy mainly the B sites under the octahedral symmetry. These findings show that the structures of TCr₂O₄ (T = Fe, Co, Ni) are very close to the normal spinel structures. Based on these findings, it is expected that Jahn-Teller (JT) effects are important in FeCr₂O₄ and NiCr₂O₄. In contrast, CoCr₂O₄ maintains the cubic structure without having the JT distortion since both Cr<SUP>3+</SUP> and Co<SUP>2+</SUP> ions are non-JT ions. This work suggests that the antiferromagnetic interaction between Cr<SUP>3+</SUP> and T<SUP>2+</SUP> ions plays an important role in determining the magnetic properties of TCr₂O₄ (T = Fe, Co, Ni).
홍석무(S. M. Hong),황지훈(J. H. Hwang),심재원(J. W. Sim),정완진(W. J. Chung),전만수(M. S. Joun) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
In this paper, a three-dimensional elastoplastic finite element analysis is conducted to reveal the fracture occurring in plate forging of a clad plate. Formability limit diagram (FLD) technique is applied in the clad material which is thin enough for FLD technique to be applied. To obtain reliable predictions, special finite element mesh system is employed. The predictions are compared with experiments, showing that they are in good agreement with each other.