• Bulletin of the Korean Chemical Society
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• 제14권4호
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• pp.465-468
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• 1993

Four compounds containing two 2,2,6,6-tetramethylpiperidin-1-yloxyl radicals were synthesized. They are all chemically bonded with squaric moieties. The diradical compounds show fundamentally the paramagnetic behaviors satisfying the theoretical magnetic susceptibility according to Curie's law. A diradical compound of salf-form 4 however shows a relatively strong antiferromagnetic interaction in comparison with other reported organic radicals. The antiferromagnetic interaction of diradical 4 approximates a value of J/k= -50 K by the theoretical analysis of its temperature dependence.

• 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.

• 한국자기학회지
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• 제19권5호
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• pp.157-160
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• 2009

Ge 원자로 구성된 1차원 체인형태의 나노클러스터에 자성전이금속 Cr 및 Mn 원자를 치환 하였을 때 자성전이금속 원자사이의 자기적 상호작용을 제1원리의 범밀도함수법을 이용하여 계산하였다. 그 결과 Ge 원자와 전이금속 원자는 반강자성적인 상호작용을 하고 있으며, Ge-Ge원자 또한 반강자성 경향을 나타내었다. 이러한 자기 교환상호작용은 Ge 원자 여러 원자 층을 자화시켜 일어나고 있으며, 그 크기도 작지 않았다. 또한 자기 교환상호작용은 Ge 원자 수에 크게 의존하였다.

• Bulletin of the Korean Chemical Society
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• 제23권9호
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• pp.1321-1324
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• 2002

• 한국자기학회지
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• 제27권4호
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• pp.140-144
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• 2017

Co 원자 4개를 포함한 cubane 구조의 분자자성체의 전자구조 및 자기적 성질을 제1원리의 범밀도함수법을 이용하여 계산하였다. 계산된 결과, Co 원자는 +2가를 가지며, 강한 내부 원자의 교환상호작용으로 high-spin 상태를 보여주었다. 스핀배열에 따른 총 에너지 계산에서 수직을 이루는 Co 원자 사이는 강자성, 더 큰 각도를 이루는 Co 원자 사이는 반강자성 교환상호작용이 일어남을 보여주었다. 이러한 원인은 $Co^{+2}(3d^7)$ 원자 사이의 초교환상호작용으로 설명할 수 있었었고, Co 분자자성체는 AFM1 = [${\uparrow}{\uparrow}{\downarrow}{\downarrow}$] 스핀구조를 가지고 있었다.

• Bulletin of the Korean Chemical Society
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• 제30권5호
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• pp.1113-1117
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• 2009

The one-dimensional coordination polymers, $[Cu^{II}(L)(NO_3)_2]_n$ (1) and {$[Cu^{II}(L)(NO_3)]{\cdot}2H_2O}_{2n} (2), were synthesized from $Cu(NO_3)_2{\cdot}3H_2O$ and 2-[(pyridin-3-ylmethyl)amino]ethanol (L, PMAE) in methanol by controlling the molar ratio of copper(II) salt. Copper(II) ion in 1 has one pyridine group of PMAE whose an aminoethanol group coordinates adjacent copper(II) ion. As the pyridine group is bonded to neighboring copper(II) ion, 1 becomes a one-dimensional chain. Contrary to 1, the structure of 2 shows that the oxygen atom of ethoxide group is bridged between two copper(II) ions, which forms a dinuclear complex. Additionally, the pyridine group of PMAE included one dinuclear unit is coordinated to the other dimeric one each other, which leads to a one-dimensional polymer. Due to the structural differences, 1 exhibits weak antiferromagnetic interaction, while 2 shows strong antiferromagnetic interaction. Due to direct spin exchange via oxygen of PMAE 2 has a much strong spin coupling than 1.

• Progress in Superconductivity
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• 제9권2호
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• pp.127-135
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• 2008

We study the effects of phonon interaction on the superconducting pairing in the high $T_c$ superconductors (HTSC). Using coupled BCS gap equations, we found that phonon interaction can induce a s-wave component to the d-wave gap, mediated by Antiferromagnetic (AFM) spin fluctuations, in the (D+iS) form. However, $T_c$ is not enhanced compared to the pure d-wave pairing without phonon interaction. On the other hand, anisotropic phonon interaction can dramatically enhance the d-wave pairing and $T_c$ itself, together with the AFM spin fluctuation interaction. This ($D_{AFM}+D_{ph}$) type pairing exhibits strongly reduced isotope coefficient despite the large enhancement of $T_c$ by phonon interaction.

• Bulletin of the Korean Chemical Society
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• 제32권3호
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• pp.1037-1040
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• 2011

The dinuclear complex 1 with cooperative hydrogen bonds can be prepared by the metal-directed reaction of Eq. (2). This work shows that the coordinated hydroxyl group trans to the secondary amino group is deprotonated more readily than that trans to the tertiary amino group and acts as the hydrogen-bond accepter. The lattice water molecules in 1 act as bridges between the two mononuclear units through hydrogen bonds. The complex is quite stable as the dimeric form even in various polar solvents. The complex exhibits a weak antiferromagnetic interaction between the metal ions in spite of relatively long Cu$\cdots$Cu distance. This strongly supports the suggestion that the antiferromagnetic behavior is closely related to the cooperative hydrogen bonds.

• Bulletin of the Korean Chemical Society
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• 제31권6호
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• pp.1704-1710
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• 2010

The structure of a 2D grid-like copper(II) complex [Cu$(NCO)_2$(pyz)](pyz=pyrazine) (1) consists of 1D chains of Cu-pyz units connected by double end-on (EO) cyanato bridges. Each Cu(II) ion has a distorted octahedral coordination, completed by the four EO cyanato and two pyrazine ligands. Magnetic interactions through EO cyanato and pyrazine bridges in 1 are discussed on the basis of DFT broken-symmetry calculations at the B3LYP level. For model dicopper(II) complexes I (bridged by cyanato) and II (bridged by pyrazine), electronic structure calculations reproduce very well the experimental couplings for the S = 1/2 ferromagnetic and antiferromagnetic exchange-coupled 2D system: the calculated exchange parameters J are +1.25 $cm^{-1}$ and -3.07 $cm^{-1}$ for I and II, respectively. The $\sigma$ orbital interactions between the Cu $x^2-y^2$ magnetic orbitals and the nitrogen lone-pair orbitals of pyrazine are analyzed from the viewpoint of through-bond interaction. The energy splitting of 0.106 eV between two SOMOs indicates that the superexchange interaction should be antiferromagnetic in II. On the other hand, there are no bridging orbitals that efficiently connect the two copper(II) magnetic orbitals in I because the HOMOs of the basal-apical NCO bridge do not play a role in the formation of overlap interaction pathway. The energy separation in the pair of SOMOs of I is calculated to be very small (0.054 eV). This result is consistent with the occurrence of weakly ferromagnetic properties in I.

• 한국자기학회지
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• 제17권5호
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• pp.215-220
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• 2007

초교환 상호작용은 MnO, $MnF_2$와 같은 전이금속 화합물에서 나타나는 반강자성을 설명하기 위해서 도입된 상호작용이다. 이 초교환 상호작용에 스핀-궤도 결합 효과를 포함시키면 비등방성 초교환(Dzyaloshinskii-Moriya: DM) 상호작용이 된다. 이 비등방성 초교환 DM 상호작용으로 ${\alpha}-Fe_2O_3$, $MnCO_3$, $CrF_3$ 등에서 나타나는 약강자성을 설명할 수 있다.