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반쪽 금속 호이슬러 화합물 Mn₃Ga의 연 X선 방사광 분광 연구
성승호(Seungho Seong),이은숙(Eunsook Lee),김현우(Hyun Woo Kim),김대현(D. H. Kim),강정수(J.-S. Kang),M. Venkatesan,J. M. D. Coey 한국자기학회 2016 韓國磁氣學會誌 Vol.26 No.6
By employing photoemission spectroscopy (PES) and soft X-ray absorption spectroscopy (XAS), the electronic structure of the candidate half-metallic antiferromagnet of Mn₃Ga Heusler compound has been investigated. We have studied two ball-milled Mn₃Ga powder samples, one after annealing and the other without annealing, respectively. Based on the Mn 2p XAS study, we have found that Mn ions are nearly divalent in Mn₃Ga and that the Mn ions having the locally octahedral symmetry and those having the locally tetrahedral symmetry are both present in Mn₃Ga. We have found relatively good agreement between the measured valence-band PES spectrum of Mn₃Ga and the calculated density of states, which is in agreement with the half-metallic electronic structure of Mn₃Ga.
마이너스 자화 스피넬 산화물의 연 X선 방사광 분광 연구
양민영(Min Young Yang),성승호(Seungho Seong),이은숙(Eunsook Lee),강정수(J.-S. Kang) 한국자기학회 2020 韓國磁氣學會誌 Vol.30 No.2
By employing soft X-ray absorption spectroscopy (XAS) and soft X-ray magnetic circular dichroism (XMCD), the electronic structures of Li<SUB>0.5</SUB>FeCr<SUB>1.5</SUB>O₄ spinel ferrite have been investigated, which exhibits the negative magnetization phenomenon. It is found that that both Fe and Cr ions are trivalent, that most of Fe3+ ions occupy the A (T<SUB>d</SUB>) sites while Cr<SUP>3+</SUP> ions occupy the B (O<SUB>h</SUB>) sites, and that the magnetic moments of Fe ions and those of Cr ions are coupled antiferromagnetically to each other. Hence Li<SUB>0.5</SUB>FeCr<SUB>1.5</SUB>O₄ can be represented as (Fe)<SUB>A</SUB>[Li<SUB>0.5</SUB>Cr<SUB>1.5</SUB>]<SUB>B</SUB>O₄.
Co가 치환된 Mn 기반 호이슬러 박막 Mn<SUB>3-x</SUB>Co<SUB>x</SUB>Ga(x = 0.56)의 연 X선 방사광 분광 연구
서연지(Yeonji Seo),성승호(Seungho Seong),강정수(J.-S. Kang) 한국자기학회 2022 韓國磁氣學會誌 Vol.32 No.1
The electronic structure of Mn<SUB>3-x</SUB>Co<SUB>x</SUB>Ga (x = 0.56) film, which is a candidate material for a half-metallic ferrimagnet, has been investigated by employing soft X-ray absorption spectroscopy (XAS), soft X-ray magnetic dichroism (XMCD), and photoemission spectroscopy (PES). According to Mn and Co 2p XAS measurements, Mn ions are divalent and have covalent bonding, while most of the substituted Co ions are in metallic states. The Co 2p XMCD spectrum of Mn<SUB>3-x</SUB>Co<SUB>x</SUB>Ga (x = 0.56) film is very similar to that of Co metal, supporting the finding of Co 2p XAS. Finite XMCD signals are found in both Co and Mn 2p XMCD spectra, but the intensity of the Mn 2p XMCD is much weaker than that of Co 2p XMCD. XMCD measurements reveal that the substituted Co ions in Mn<SUB>3-x</SUB>Co<SUB>x</SUB>Ga (x = 0.56) form ferromagnetic metallic clusters and induce weak polarization in Mn ions. Hence, this study suggests that ferromagnetic metallic Co clusters play an important role in determining the magnetic properties of Mn<SUB>3-x</SUB>Co<SUB>x</SUB>Ga (x = 0.56) films.
염료감응 태양전지 전극용 반도체 나노 물질의 광전자분광 연구
김현우(Hyun Woo Kim),이은숙(Eunsook Lee),김대현(D. H. Kim),성승호(Seungho Seong),강정수(J.-S. Kang),문수연(S. Y. Moon),신유주(Yuju Shin) 한국자기학회 2015 韓國磁氣學會誌 Vol.25 No.5
The electronic structures of the potential candidate semiconductor nanoparticles for dye-sensitized solar cell (DSSC), such as ZnSnO₃ and Zn₂SnO₄, have been investigated by employing X-ray photoemission spectroscopy (XPS). The measured X-ray diffraction patterns show that ZnSnO₃ and Zn₂SnO₄ samples have the single-phase ilmenite-type structure and the inverse spinel structure, respectively. The measured Zn 2p and Sn 3d core-level XPS spectra reveal that the valence states of Zn and Sn ions are divalent (Zn 2+) and tetravalent (Sn 4+), respectively, in both ZnSnO₃ and Zn₂SnO₄. On the other hand, the shallow core-level measurements show that the binding energies of Sn 4d and Zn 3d core levels in ZnSnO₃ are lower than those in Zn₂SnO₄. This work provides the information on the valence states of Zn and Sn ions and their chemical bonding in ZnSnO₃ and Zn₂SnO₄.
Pd층의 두께 변화에 따른 [Co/Pd] 다층박막의 연엑스선 방사광 분광 연구
김대현(D. H. Kim),이은숙(Eunsook Lee),김현우(Hyun Woo Kim),성승호(Seungho Seong),강정수(J.-S. Kang),양승모(Seung-Mo Yang),박해수(Hae-Soo Park),홍진표(JinPyo Hong) 한국자기학회 2016 韓國磁氣學會誌 Vol.26 No.4
We have investigated the electronic structures of intermetallic multilayer (ML) films of [Co(2Å)/Pd(xÅ)] (x: the thickness of the Pd sublayer; x = 1 Å, 3 Å, 5 Å, 7 Å, 9 Å) by employing soft X-ray absorption spectroscopy (XAS) and soft X-ray magnetic circular dichroism (XMCD). Both Co 2p XAS and XMCD spectra are found to be similar to one another, as well as to those of Co metal, providing evidence for the metallic bonding of Co ions in [Co/Pd] ML films. By analyzing the measured Co 2p XMCD spectra, we have determined the orbital magnetic moments and the spin magnetic moments of Co ions in [Co(2Å)/Pd(xÅ)] ML films. Based on this analysis, we have found that the orbital magnetic moments are enhanced greatly when x increases from 1 Å to 3 Å, and then do not change much for x ≥ 3 Å. This finding suggests that the interface spin-orbit coupling plays an important role in determining the perpendicular magnetic anisotropy in [Co/Pd] ML films.