• Bulletin of the Korean Chemical Society
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• 제11권2호
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• pp.85-88
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• 1990

The electron paramagnetic resonance (EPR) spectrum of the copper (II) complex with the 2-methylamino-1-cyclo-pentene-1-dithiocarboxylate (acdc) anion, $Cu(N-CH_3acdc)_2$ has been studied in the diamagnetic host lattices afforded by the corresponding divalent nickel, zinc, cadmium and mercury complexes. EPR parameters of the complex support the exclusive use of sulfur atoms by the ligand in metal binding. A combination of host lattice structure and covalency effects can be account for the observed spin-Hamiltonian parameters.

• 대한자기공명의과학회:학술대회논문집
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• 대한자기공명의과학회 1999년도 제4차 추계학술대회 초록집
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• pp.53-53
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• 1999

• Bulletin of the Korean Chemical Society
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• 제18권10호
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• pp.1090-1093
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• 1997

The solvent effects on the isotropic NMR shifts in conformationally rigid ligands such as quinuclidine, pyridine, and 4-aminopyridine coordinated to the paramagnetic polyoxometalate, [SiW11CoⅡO39]6- (SiW11Co), are reported. For these complexes the ligand exchange is slow on the NMR time scale and pure 1H NMR signals have been observed at room temperature. The signals for the SiW11Co complexes are shifted upfield whe dimethyl sulfoxide-d6 (DMSO) is added to a D2O solution. The isotropic shifts are separated into contact and pseudocontact contributions by assuming that the contact shifts are proportional to the isotropic shifts of the same ligands coordinated to [SiW11NiⅡO39]6-. It is shown that both the contact and pseudocontact shifts decrease (the absolute values of the pseudocontact shifts increase), when D2O is replaced by DMSO. It is suggested that D2O, a strong hydrogen bond donor, withdraws electron density from [SiW11CoⅡO39]6-, increasing the acidity of the cobalt ion toward the axial ligand. When D2O is replaced by DMSO, the acidity of the cobalt ion in SiW11Co decreases, weakening the Co-N bond. Then both the contact and pseudocontact shifts are expected to decrease in agreement with the observed solvent effects.

• Journal of the Korean Physical Society
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• 제73권10호
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• pp.1555-1560
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• 2018

$AlFe_2B_2$ produced by using a conventional arc melter has a ferromagnetic material with a Curie temperature ($T_C$) of around 300 K, but the arc-melt generates paramagnetic $Al_{13}Fe_4$ impurities during the synthesis of $AlFe_2B_2$. Impurities are brought to cause a decrease in magnetocaloric effects (MCEs). To investigate the effects of $Al_{13}Fe_4$ impurities on MCEs, we prepared and compared ascast and acid-treated samples, where the acid treatment was performed to remove the $Al_{13}Fe_4$ impurities. For the structural analysis, powder X-ray diffraction was carried out, and the measured data were subjected to a Rietveld refinement. The presence of $Al_{13}Fe_4$ impurities in the as-cast sample was observed in the phase analysis measurements. Magnetic properties were investigated by using Superconducting Quantum Interference Device (SQUID) measurements for the as-cast and the acid-treated $AlFe_2B_2$ samples. From isothermal magnetization measurements, Arrott plots were obtained showing that the transition of $AlFe_2B_2$ has a second-order magnetic phase transition (SOMT). The $T_C$ and the saturation magnetization increased for the acid-treated sample due to removal of the paramagnetic impurities. As a consequence, the magnetic entropy change ($-{\Delta}S$) increased in the pure $AlFe_2B_2$ samples, but the full width at half maximum in the plot of $-{\Delta}S$ vs. T decreased due to the absence of impurities.

• 한국자기공명학회논문지
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• 제24권2호
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• pp.47-52
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• 2020

Liquid-liquid phase separation (LLPS) of biomolecules, a newly-found phase behavior of molecules in the liquid phase, has shown to its relationship to various biological function and misfolding diseases. Extensive studies have increasingly revealed a general mechanism of LLPS and characterized the liquid droplet; ho wever, intermolecular interactions of proteins and structural states of LLPS-inducing proteins inside of the droplet remain largely unknown. Solution NMR spectroscopy has emerged as a powerful approach as it provides invaluable information on protein intermolecular interactions and structures at the atomic and residue level. We herein comprehensively address useful techniques of solution NMR including the effect of paramagnetic relaxation enhancement for the study on the LLPS and droplet based on recent studies.

• Bulletin of the Korean Chemical Society
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• 제18권4호
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• pp.369-373
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• 1997

When 1H NMR spectra of pyridine, 4-amino-, 4-methyl-, and 4-cyanopyridine coordinated to the paramagnetic polyoxometalate, [SiW11CoⅡO39]6- in D2O are compared, both α- and β-proton peaks are shifted upfield as the basicity of the ligand decreases. The isotropic shifts are separated into contact and pseudocontact contributions by assuming that the contact shifts are proportional to the isotropic shifts of the same ligands coordinated to [SiW11NiⅡO39]6-. This separation reveals that the shift variations with the axial ligand basicity are dominated by changes in the magnetic anisotropy (pseudocontact shift) of [SiW11CoⅡ(ptl)O39]6- (ptl=pyridine-type ligand). The magnitude of the magnetic anisotropy in a series of pyridine-type ligands increases linearly as the pKa of their conjugate acids decreases.

• 한국자기학회지
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• 제15권3호
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• pp.177-180
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• 2005

Czochralski방법을 사용하여 정비조성(stoichiometric)으로 성장시킨 강유전체 $LiTaO_3$, 단결정을 $1000^{\circ}C$ 및 $1100^{\circ}C$에서 각각 열처리하였다. 열처리한 시료와 열처리하지 않은 정비조성 $LiTaO_3$ 단결정에 대하여 전자 상자성 공명(EPR : electron paramagnetic resonance) 실험을 하였다. X-band(9.21 GHz) 전자 상자성 공명 스펙트로미터를 사용하여 얻은 $Fe^{3+}$ 상자성 불순물 이온의 공명 흡수선을 분석한 결과 정비조성 $LiTaO_3$ 단결정내의 $Fe^{3+}$ 상자성 불순물 이온의 위치(site location)와 국소 대칭성(local site symmetry)은 열처리 후에도 변화가 없는 것을 알 수 있었다. 그러나 $1000^{\circ}C$및 $1100^{\circ}C$에서 열처리 한 단결정의 경우에는 $v$ 이온이 $Fe^{2+}$ 이온으로 원자가 상태가 바뀌는 것을 화인 하였다. 또한 유효 스핀 하밀토니안을 이용하여 EPR 상수를 계산하였다.

• 비파괴검사학회지
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• 제19권1호
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• pp.1-7
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• 1999

교류전위차법 (alternating current potential drop : ACPD)을 이용하여 이차원 표면균열을 갖고 있는 상자성체 (paramagnetic material)의 모드 I (opening mode) 응력확대계수($K_I$)를 실험적으로 평가하기 위하여 하중에 따른 교류전위차 변화(change in ACPD)를 연구하였다. 아울러 하중에 의한 전위차 변화의 원인 그리고 전위차 변화에 미치는 자속(magnetic flux) 탈자(demagnetization) 및 균열길이의 영향을 연구하였다. 상자성체의 교류전위차는 인장하중을 증가시킬수록 선형적으로 감소하였다. 전위차 감소의 원인은 균열선단 주위의 도전율(conductivity)이 인장하중의 증가에 따라 증가하고 이는 시험편의 저항과 내부 인덕턴스를 감소시키기 때문이다. 도전율의 변화는 균열선단 주변의 응력상태에 의존하기 때문에 일정 $K_I$ 변화에 따른 전위차 변화량은 균열길이에 의존하지 않는다. 하중에 의한 전위차변화량은 시험편 주위의 자속의 유무에 영향을 받지만 탈자의 유무에는 영향을 받지 않는다.

• 한국재료학회지
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• 제3권1호
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• pp.3-6
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• 1993

Gd박막의 강자성-상자성 상전이 온도(Tc)이동을 조사했다. 강자성-상자성 상전이 온도에서 전기저항이 변화되는 변곡점을 관측하여 Tc를 결졍하였는데, 두께가 6600$\AA$인 Gd박막의 상전이 온도는 bulk상태의 Gd의 전이온도보다 4$\pm$0.$3^{\circ}C$정도 아래로 이동됨을 알았다. 이것은 강자성 Gd박막의 Tc이동에 대한 최초의 측정이며, 실험과 finite-sime scaling이론을 비교 분석했다.

• 한국표면공학회지
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• 제29권6호
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• pp.847-850
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• 1996

The bi-layered films composed of Co-Cr-Ta layers and paramagnetic $Co_{67}Cr_{33}$ underlayer were deposited by suing Facing Targets Sputtering(FTS). The effects of $Co_{67}Cr_{33}$ underlayer on the crystallographic and magnetic characteristics of the Co-Cr-Ta layer deposited on the underlayer was investigated. The diffraction intensity $I_{p(002)}$ of Co-Cr-Ta layers on the $Co_{67}Cr_{33}$ layer was stronger than that of single layer and Co-Cr-Ta/Ti double layer. Therefore, the crystallinity of Co-Cr-Ta layer was imporved by the $Co_{67}Cr_{33}$ underlayer rather than Ti ones. However, te coercivity H$_{c\bot}$ of Co-Cr-Ta layers deposited on $Co_{67}Cr_{33}$ underlayer was as low as 250 Oe even at substrate temperature of $220^{\circ}C$. This H$_{c\bot}$ decrease seems to be attributed to the effect of the $Co_{67}Cr_{33}$ underlayer as well as interval time between deposition of the underlayer and the Co-Cr-Ta layer.