• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.81-81
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• 2012

XMCD (X-ray Magnetic Circular Dichroism)는 원형 편광 X-선의 helicity 방향이 시료의 자화 방향과 평행, 또는 반평행할 때 시료의 색이 바뀌는 현상, 즉 흡수율이 달라지는 현상이다. XMCD측정이 가지는 장점은 첫째, 이 실험이 특정 원소의 흡수선에서 이루어지기 때문에 시료 전체에서 특정 원소에 의한 자기적 성질을 분리해서 측정할 수 있을 뿐만 아니라, 같은 원소라 하더라도 다른 화학적 환경에 있는 원자들의 자기적 성질의 분리가 가능하다는 점이다. 이러한 성질로 인해 XMCD는 다른 원소들로 이루어진 다층 박막(GMR, TMR 등의 자기저항박막 구조물)의 층별 자기적 성질 연구 및 신자성물질의 자기적 성질의 고유성 연구에 많이 이용되었다. XMCD가 가지는 두 번째 장점은 sum rule을 통하여 자기 모멘트의 두 가지 성분인 궤도 모멘트(orbital moment)와 스핀 모멘트(spin moment)의 구별이 가능하다는 점이다. 이러한 장점은 수직자기 메모리 연구 및 스핀과 격자 간의 상호작용이 중요한 역할을 하는 다강체 등의 연구에 많이 이용되어 왔다. XMCD 측정이 또 다른 장점이 될 수 있는 것은 표면에 대단히 민감하다는 점이다. VSM, SQUID 등의 측정방법으로는 시료의 체적이 대단히 작은 수 ${\AA}$ 정도의 초박막에 대해서는 충분한 민감도를 가질 수 없다. 그러나, XMCD의 측정 깊이는 수십 ${\AA}$ 정도로 표면에 민감하기 때문에 이러한 초박막에 대해서도 충분한 민감도를 가질 수 있어서 SMOKE(Surface Magneto-Optical Kerr Effect)와 표면 자성연구에 있어서 독보적인 장치로 이용되어 왔다. 이러한 장점으로 인해 XMCD는 1990년대 이후 분광학적으로 활발히 이용되어 왔을 뿐만 아니라, 대단히 빠르고 신호가 큰 현상이기 때문에 최근 들어서는 자구(magnetic domain) 관찰 등을 목적으로 한 자기 현미경 및 자기현상의 동역학 연구에도 많이 응용되고 있다. 이 강연에서는 이러한 X-선 자기 원형 이색성 현상의 원리 및 실험 방법 등을 설명하겠다. 또한 몇 가지 X-선 자기 원형 이색성을 이용한 최근 몇 가지 연구도 소개하려 한다.

• Journal of the Korean Magnetics Society
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• v.26 no.4
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• pp.124-128
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• 2016

We have investigated the electronic structures of intermetallic multilayer (ML) films of [$Co(2{\AA})/Pd(x{\AA})$] (x: the thickness of the Pd sublayer; x = $1{\AA}$, $3{\AA}$, $5{\AA}$, $7{\AA}$, $9{\AA}$) 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 [$Co(2{\AA})/Pd(x{\AA})$] ML films. Based on this analysis, we have found that the orbital magnetic moments are enhanced greatly when x increases from $1{\AA}$ to $3{\AA}$, and then do not change much for $x{\geq}3{\AA}$. This finding suggests that the interface spin-orbit coupling plays an important role in determining the perpendicular magnetic anisotropy in [Co/Pd] ML films.

• Journal of the Korean Chemical Society
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• v.24 no.4
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• pp.269-279
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• 1980

A method for calulation of the magnetic moments for both octahedral and distorted octahedral $[V(III)A_3B_3]$ type complexes, all with $t^2_2$ configuration, has been developed [A and B = O, Cl, N, F or Br]. The calculated magnetic moments by this method are in reasonable agreements with the experimental values. The calculated magnetic moments for distorted octahedral $[V(III)A_3B_3]$/TEX> type complexes decrease as the extent of tetragonal distortion increases.The effects of k (orbital reduction faction factor), $\xi'$/TEX> and temperature on the magnetic moments are also investigated.A new method for calculation of the contribution of $^3T_1$ molecular orbitals to the dipole moment and polarizability has also developed. The calculated contribution of $^3T_1$ molecular orbitals falls in the reasonable range of values.

• Journal of Magnetics
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• v.14 no.3
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• pp.114-116
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• 2009

The electronic properties of Cu or Pd-doped GaN at several concentrations are examined using the full-potential linear muffin-tin orbital method. For ($Cu_{0.055}Ga_{0.945}$)N, the model reveals a magnetic moment of $1.47{\mu}B$ per supercell. The range of concentrations that are spin-polarized should be restricted within narrow limits. A paramagnetic to ferromagnetic phase transition is found to occur at a Cu concentration of 5.55%.

• Current Applied Physics
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• v.18 no.11
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• pp.1190-1195
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• 2018

By employing soft X-ray magnetic circular dichroism (XMCD), soft X-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES), we have investigated the electronic structure of the candidate zero-moment half-metallic $Mn_3Ga$. We have studied the ball-milled and annealed $Mn_3Ga$ powder samples that exhibit nearly zero magnetization. Mn 2p XAS revealed that Mn ions in $Mn_3Ga$ are nearly divalent for both of the Mn ions having the locally octahedral symmetry and those having the locally tetrahedral symmetry. The measured Mn 2p XMCD spectrum of $Mn_3Ga$ is very similar to that of ferrimagnetic $MnFe_2O_4$ having divalent Mn ions. The sum-rule analysis of the Mn 2p XMCD spectrum shows that both the spin and orbital magnetic moments of Mn ions in $Mn_3Ga$ are negligibly small, in agreement with the nearly compensated-ferrimagnetic ground state of $Mn_3Ga$. The valence-band PES spectrum of $Mn_3Ga$ agrees well with the calculated density of states, supporting the half-metallic electronic structure of $Mn_3Ga$.

• Journal of the Korean Magnetics Society
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• v.4 no.2
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• pp.100-105
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• 1994

Ni-Fe thin films are deposited on the corning glass substrate by means of RF magnetron sputtering system In order to investigate the dependence of the prorerties of Ni-Fe thin films on the film thickness, ferromagnetic reson¬ance spectrum has been examined. The effective magnetization $M_{eff}$ is constant for all samples, while the exchange stiffness constant A increases with the film thickness. A tendency that spectroscopic splitting factor g increases with the sample thickness, we expect that the increase of the contribution of the orbital motion to the magnetic moment as a reason for it.

• Journal of Magnetics
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• v.20 no.4
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• pp.331-335
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• 2015

The ferromagnetic and electronic structure for the $Al_xGa_{1-x}P$ and Mn-doped $AlGaP_2$ was studied by using the self-consistent full-potential linear muffin-tin orbital method. The lattice parameters of un-doped $Al_xGa_{1-x}P$ (x = 0.25, 0.5, and 0.75) were optimized. The band-structure and the density of states of Mn-doped $AlGaP_2$ with or without the vacancy were investigated in detail. The P-3p states at the Fermi level dominate rather than the other states. Thus a strong interaction between the Mn-3d and P-3p states is formed. The ferromagnetic ordering of dopant Mn with high magnetic moment is induced due to the (Mn-3d)-(P-3p)-(Mn-3d) hybridization, which is attributed by the partially filled P-3p bands. The holes are mediated with keeping their 3d-characters, therefore the ferromagnetic state is stabilized by this double-exchange mechanism.

• Journal of Powder Materials
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• v.13 no.6 s.59
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• pp.401-407
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• 2006

Effects of oxygen deficiency on the room temperature ferromagnetism in Fe-doped reduced $TiO_2$ have been investigated by comparing the air-annealed $Ti_{0.97}Fe_{0.03}O_2$ compound with secondly post-annealed one in vacuum ambience. The air-annealed sample showed a paramagnetic behavior at room temperature. However, when the sample was further annealed in vacuum, a strongly enhanced ferromagnetic behavior was observed at same temperature. $M{\"{o}}ssbauer$ spectra of air-annealed sample at 295K showed a single doublet of $Fe^{3+}$, suggesting that the Fe ions are paramagnetic. On the other hand, the absorption spectra after vacuum-annealing exhibited two doublets, in which one is the same component with air-annealed sample and the other is new doublet corresponding to $Fe^{2+}$ state. This result suggests that the occurrence of ferromagnetism in reduced sample may be interpreted as the contribution of unquenched orbital moment of $Fe^{2+}$ ions.

• Journal of the Korean Chemical Society
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• v.56 no.6
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• pp.679-691
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• 2012

New series of metal complexes of Co(II), Ni(II), Cu(II), Zn(II), Pd(II) and Pt(II) with 4-(p-chlorophenyl)-1-(pyridin-2-yl)thiosemicarbazide (HCPTS) have been synthesized and characterized by elemental analyses, magnetic moment, spectra (IR, UV-Vis, $^1H$ NMR, mass and ESR) and thermal studies. The IR data suggest different coordination modes for HCPTS which behaves as a monobasic bidentate with all metal ions except Cu(II) and Zn(II) which acts as a monobasic tridentate. Based on the electronic and magnetic studies, Co(II), Cu(II), Pd(II) and Pt(II) complexes have square - planner, Ni(II) has mixed stereochemistry (tetrahedral + square planar), while Zn(II) is tetrahedral. Molar conductance in DMF solution indicates the non-ionic nature of the complexes. The ESR spectra of solid copper(II) complex show $g_{\parallel}$ (2.2221) > $g_{\perp}$ (2.0899) > 2.0023 indicating square-planar structure and the presence of the unpaired electron in the $d_x2_{-y}2$ orbital with significant covalent bond character. The thermal stability and degradation kinetics of the ligand and its metal complexes were studied by TGA and DTA and the kinetic parameters were calculated using Coats-Redfern and Horowitz-Metzger methods. The complexes have more antibacterial activity against some bacteria than the free ligand. However, the ligand has high anticancer activities against HCT116 (human colon carcinoma cell line) and HEPG2 (human liver hepatocellular carcinoma cell line) compared with its complexes.

• Journal of the Korean Magnetics Society
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• v.18 no.6
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• pp.211-216
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• 2008

The effects of Si impurity on electronic structures and magnetism of bcc Fe are investigated by using a first-principles method by considering spin-orbit coupling. In order to describe the Si impurity, a 27 atomic bcc Fe supercell has been considered. The Kohn-Sham equation was solved in terms of the all-electron full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA). The effects of spin-orbit coupling were calculated self-consistently by considering spin-diagonal terms based on second variation method. For the ferromagnetic (FM) state without considering SOC, the spin magnetic moment of the Si impurity was calculated to be $-0.143{\mu}B$, while the magnetic moments of Fe atoms were calculated to be $2.214{\mu}B$, $2.327{\mu}B$, and $2.354{\mu}B$ in away from the Si atom, respectively. However, the FM state with considering SOC, the spin magnetic moment of the Si impurity was calculated to be $-0.144{\mu}B$, which is not affected significantly by SOC, but the spin magnetic moments of Fe atoms were calculated $2.189{\mu}B$, $2.310{\mu}B$, and $2.325{\mu}B$, respectively, which are much reduced value compared to those of the FM state without SOC. Comparing the total charge density and spin density, those features are thought to be originated by the screening distortions of the Fe $t_{2g}$ orbital, which can be obtained by considering SOC.