• Bulletin of the Korean Chemical Society
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• 제33권7호
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• pp.2338-2340
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• 2012

The spin exchange parameters of $VOSb_2O_4$ were evaluated by performing energy-mapping analysis based on density functional calculations. The spin exchange interaction between the nearest-neighbor $V^{4+}$ ions is strongly antiferromagnetic while other interactions are negligible. Thus, the magnetic structure of $VOSb_2O_4$ is best described by a spin-1/2 Heisenberg antiferromagnetic chain with no spin frustration.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1277-1278
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• 2014

• Bulletin of the Korean Chemical Society
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• 제15권5호
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• pp.347-349
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• 1994

The Oguchi theory of antiferromagnetism has been modified for antiferromagnetically interacting spin-pair systems with anisotropic exchange interaction. The parallel and perpendicular susceptibilities $({\chi}_{\parallel}\;and\;{\chi}_{\perp})$ have been expressed as functions of exchange interactions $(J_z\;and\;{\gamma}=J_x/J_z)$, anisotropic molecular field parameters $({\kappa}\;and\;{\kappa}_x)$, $g_z\;and\;g_x$. In contrast to the previous theories, the parallel susceptibilities are not the same as the perpendicular susceptibilities above Neel temperature $T_N$.

• Journal of Magnetics
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• 제9권2호
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• pp.60-64
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• 2004

In this paper calculations of magnetisation and magnetoresistance characteristics of the Spin Valve (SV) and Pseudo Spin Valve (PSV) spintronics structures are reported and compared with the experimental data. The magnetisation reversal process was analysed with respect to the Stoner- Wohlfahrt model of total surface energy in terms of uniaxial anisotropy, exchange coupling between ferromagnetic layers, unidirectional exchange anisotropy of pinned layer (modelled by exchange coupling between magnetisation of pinned layer and net magnetisation of antiferromagnetic layer with high anisotropy). The numerical simulation of the model to the experimental magnetisation data yielded the above parameters for SV and PSV structures. These parameters were used to more sophistically micromagnetic modelling tool originating from the project called Object Oriented Micromagnetic Framework. Influence of the shape anisotropy of the Magnetic Tunnelling Junction cell used in MRAM was simulated by means of micromagnetic simulations. Results were compared to those obtained from the spot Kerr measurements.

• 한국자기학회지
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• 제10권2호
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• pp.86-92
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• 2000

자성 박막 표면에서의 일축 자기이방성을 고려한 자화의 경계조건을 Maxwell 방정식과 자화에 대한 Gilbert 방정식을 동시에 만족하는 해에 적용하여 자성박막에서 여기되는 스핀파 공명신호에 대한 모의실험을 수행하였다. 공명신호에 영향을 주는 물리량은 박막두께, 교환강성 상수, 표면 자기이방성 상수, 포화자화, 감쇠 상수, 전기비저항 등이며, 이러한 물리량들이 자성 박막에서 여기되는 스핀파 거동에 미치는 영향을 공명흡수선의 공명자기장, 선폭, 세기로 구분하여 조사하였다.

• 대한화학회지
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• 제36권3호
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• pp.345-350
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• 1992

Ln$(NO_3)_3$/DMF 상자성 용액의 양성자 선-나비와 화학적이동을 240 K부터 380 K 사이에서 측정하였다. 이들 데이터로부터 DMF 분자의 CHO기에 대한 배위구 교환속도와 열역학 교환파라미터를 추출하였다. 1/$T_2$ 와 ${\Dellta}{\omega}$ 데이터의 온도의존성을 자세하게 분석하고 고찰하여 결과를 정리하였다. 분석의 결과를 살펴보면 짝짓지 않은 전자 스핀이 몇몇 $Ln^{3+}$이온에서 첫 배위구를 넘어 퍼지면서 bulk 용매의 DMF 분자로 스칼라이완의 기여를 제공하는 것 같다.

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1373-1380
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• 2019

Besides promising implications as fertile nuclear materials, thorium carbonitrides are of great interest owing to their peculiar physical and chemical properties, such as high density, high melting point, good thermal conductivity. This paper reports first-principles simulation results on the structural, electronic and magnetic properties of cubic thorium carbonitrides $ThC_xN_{(1-x)}$ (X = 0.03125, 0.0625, 0.09375, 0.125, 0.15625) employing formalism of density-functional-theory. For the simulation of physical properties, we incorporated full-potential linearized augmented plane-wave (FPLAPW) method while the exchange-correlation potential terms in Kohn-Sham Equation (KSE) are treated within Generalized-Gradient-Approximation (GGA) in conjunction with Perdew-Bruke-Ernzerhof (PBE) correction. The structural parameters were calculated by fitting total energy into the Murnaghan's equation of state. The lattice constants, bulk moduli, total energy, electronic band structure and spin magnetic moments of the compounds show dependence on the C/N concentration ratio. The electronic and magnetic properties have revealed non-magnetic but metallic character of the compounds. The main contribution to density of states at the Fermi level stems from the comparable spectral intensity of Th (6d+5f) and (C+N) 2p states. In comparison with spin magnetic moments of ThSb and ThBi calculated earlier with LDA+U approach, we observed an enhancement in the spin magnetic moments after carbon-doping into ThN monopnictide.

• 한국자기학회지
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• 제3권3호
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• pp.179-184
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• 1993

비정질 합금 $Fe_{78}Si_{9}B_{13}$의 구조를 X-선 회절상을 분석하여 구하였다. 계산된 동경분포함수(RDF)의 첫번째 peak는 최인접 원자의 분포를 나타내는 것으로 Gaussian 함수형태를 나타낸다. 구조분석에서 본 시료의 최인접 원자배위수는 13.5이고, 최인접 원자간 평균거리 $r_{0}$는 $2.595{\AA}$, 인접원자들의 분포를 나타내는 Gaussian 함수의 변수 ${\delta}r$은 $0.27{\AA}$이다. 저온에서의 포화자화의 온도 의존성은 spin 파로 설명할 수 있으며, 이 때에 계산된 spin파 stiffness 상수는 $117.8\;meV\;{\AA}^2$ 이다. 또한, 포화자화의 온도 의존성을 Handrich의 분자장 이론식과 맞추어 얻은 변수는 각각 S=1/2 일때 ${\Delta}=0.32$이고, S=1 일때 ${\Delta}=0.23$으로 이론식과 실험결과가 전체적으로 잘 일치한다. 구조분석 결과와 분자장 이론식에서 구한 변수를 활용하여 spin파 stiffness 상수를 계산할 수 있으며, 이로써 구한 값은 S=1/2일때 $149\;meV\;{\AA}^2$ 이고, S=1 일 때 $138\;meV\;{\AA}^2$ 이다. 또한, 평균 교환결합상수 J($r_{0}$)는 S=1/2일때 17.9 meV이고, S=1일때는 J($r_{0}$)는 6.7 meV 으로 추정된다.

• 한국자기학회지
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• 제5권5호
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• pp.679-682
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• 1995

The observed high-field magnetization curves of $Sm_{2}Fe_{17}N_{3.0}$ at 4.2 K and 296 K are well reproduced by the calculation using the Sm-Fe exchange field $2\mu\textrm{B}H_{ex}\;=\;320\;K$ and two crystalline electric field parameters ${A_{0}}^{2}=\;-910\;K$ and ${A_{1}}^{0}=\;200\;K$. The calculation shows that during the magnetization process along the hard axis at 4.2 K, the Sm moment rotates toward the direction antiparallel to H when H < 110 kOe and then returns to the field direction with further increase of the field. At 296 K, the Sm moment rotates toward the direction antiparallel to H monotonously with increasing field and finally becomes antiparallel to H when $H{\geq}H_{A}=210\;kOe$. The particular magnetization process of the Sm moment can be explained by the field-induced noncollinear coupling between the spin and orbital moments of the Sm ion.

• Bulletin of the Korean Chemical Society
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• 제17권1호
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• pp.46-50
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• 1996

Monoanionic nickel(Ⅲ) complexes, [Ni(dmbit)2]1- and [Ni(dmbbip)2]1- where dmbit2- and dmbbip2- denote 2-thiobenzo[d]-1,3-dithiole-5,6-dithiolate and 1,2-bis(isopropylthio)benzen-4,5-dithiolate, respectively, have been synthesized by the iodine oxidation of dianionic complexes. In the scanning electron microscopic(SEM) images, these complexes show the well-grown two-dimensional layered structures which are clearly comparable to the dianionic ones with three-dimensional structures. Magnetic susceptibilities of nickel(Ⅲ)complexes are fitted well with the two-dimensional Heisenberg antiferromagnet model of S=1/2 system resulting in the spin-exchange parameters (|J|/k) of 11.4 K and 0.45 K, respectively. The weaker magnetic interaction in [Ni(dmbbip)2]1- is resulted from the bulky isopropyl groups on the periphery of dmbbip ligand. EPR measurements for [Ni(dmbit)2]1- give the signal with axial symmetry and the anisotropic g-values for low-spin nickel(Ⅲ) (g//=2.158, g =2.030,gav=2.074 at 300 K; g//=2.162, g =2.038, gav=2.080 at 77 K). It is therefore concluded that nickel(Ⅱ) is oxidized to nickel(Ⅲ), rather than dmbit2- and dmbbip2- ligands are, by the iodine oxidation. The paramagnetic Ni(Ⅲ) would be located in the axial symmetry(D4h) with the electronic configuration of (dxz2dyz2dz22dxy1dx2-y20).