다중강전자 상태를 가진 육방정계물질의 전자구조 계산

박기택,Park, Key-Taeck 한국자기학회 2007 韓國磁氣學會誌 Vol.17 No.4

다중강전자 상태의 $YMnO_3,\;ScMnO_3$의 전자구조와 자기구조를 국소스핀밀도근사(LSDA)를 이용하여 계산하였다. 강자성 상태이며 강유전 상태의 전자구조는 육방정계 구조로 인하여 Mn 3d 에너지띠가 분리되어 띠틈을 나타내었다. 이러한 에너지 띠틈과 작은 Y, Sc 이온의 반경으로 인하여 $YMnO_3,\;ScMnO_3$는 반강자성 강유전적 성질을 가지는 다중강전자 구조를 가지고 있음을 보았다. 또한 총에너지 계산을 통하여 반강자성, 강유전 상태가 가장 안정됨이 실험과 일치하였다. We have studied electronic structures and magnetic properties of $YMnO_3,\;ScManO_3$ with hexagonal structure using Full Potential Linearized Augmented Plane Wave (FLAPW) method based on LSDA method. LSDA calculation results show that multiferroic $YMnO_3$ shows energy gap due to hexagonal symmetry and magnetic interaction. Because of insulating gap and small Y ion, $YMnO_3$ shows magnetic and ferroelectric state. However, $ScMnO_3$ does not show the energy gap because of strong hybridization of Mn-O for LSDA calculation. We confirmed the stability of multiferroic state for $YMnO_3\;and\;ScManO_3$ using total energy calculations. The antiferromagnetic and ferroelectric states have the lowest energy about 100 meV.

이중 페로브스카이트 구조 La₂MnFeO6의 전자구조와 자기구조 계산

박기택(Key-Taeck Park) 한국자기학회 2000 韓國磁氣學會誌 Vol.10 No.3

We present results based on FLAPW local spin density(LSD) calculations of double perovskite structure oxide La₂MnFeO_6. The total energy calculations with various spin structures show that this material has a stable ferromagnetic spin configuration. The ionic state of transition metals depend on the spin configuration (Mn⁴+ and Fe²+ for ferromagnetic structure, Mn³+ and Fe³+ for ferrimagnetic structure). It is explained by super exchange interaction between transition metals. The calculated magnetic structure is well matched with recent experimental result.

이중 철 효소의 전자구조 및 자기구조 계산

박기택(Key Taeck Park) 한국자기학회 2015 韓國磁氣學會誌 Vol.25 No.4

We have studied electronic and magnetic structure of 2 kinds of diiron molecules using OpenMX method based on density functional method. The calculated density of states of diiron-2 is similar with that of diiron-4 because of equal number of 6 ligand atoms. The calculated total energy with antiferromagnetic spin configuration is lower than those of ferromagnetic configurations for both of them. The exchange interaction J of diiiron-4 between Fe<SUP>+3</SUP> atoms is one order larger than that of diiron-2, and the calculated J matches well with the experimental one. That comes from the short distance of Fe-O and the high O 2p energy levels. It derives a strong super exchange interaction. The angle of diiron-4 between Fe atoms is bigger than that of diiron-2. It also derives a strong super exchange interaction because of the σ-bond between Fe and O atoms.

자성 원자를 치환한 1차원 클러스터의 전자구조 및 자성구조 계산

박기택(Key Taeck Park) 한국자기학회 2009 韓國磁氣學會誌 Vol.19 No.5

We have studied electronic structures and magnetic properties of one dimensional Ge chain nanoclusters using OpenMX method based on densty functional method. The calculation results show the strong antiferromagnetic interaction between Cr and Ge atoms. The magnetic interaction between Ge and Ge atoms are almost antiferromagnetic behaviors. The magnetic exchange interaction are occurred over the sevaral Ge atom layers. The magnitude of this interaction depends number of Ge atom.

Cubane-type Mn₄ 클러스터의 전자구조 및 자기구조 계산

박기택(Key Taeck Park) 한국자기학회 2012 韓國磁氣學會誌 Vol.22 No.4

We have studied electronic and magnetic structure of cubane-type Mn4 cluster using OpenMX method based on density functional method. The calculated density of states shows that the octahedron of O atoms split e<SUB>g</SUB> and t<SUB>2g</SUB> energy levels like bulk MnO with cubic structure. Total energy with antiferromagnetic spin configuration is lower than those of other spin configurations because of super exchange interaction. Calculated exchange interaction J between Mn atoms with anti-parallel spin is larger than between Mn atoms with parallel spin.

Cubane 구조를 가진 Cu<SUB>4</SUB> 분자자성체의 전자구조 계산

박기택(Key Taeck Park) 한국자기학회 2016 韓國磁氣學會誌 Vol.26 No.4

We have studied electronic and magnetic structure of cubane-type Cu magnetic molecule using density functional method. The calculated density of states show that Cu has 3d x<SUP>2</SUP>-y<SUP>2</SUP> hole orbital because of short distances between Cu atom and in-plane 4 ligand atoms. The calculated total energy with in-plane antiferromagnetic spin configuration is lower than those of ferromagnetic configurations. The calculated exchange interaction J between in-plane Cu atoms is much larger than those between out-plane Cu atoms, since the x<SUP>2</SUP>-y<SUP>2</SUP> hole orbital ordering of Cu 3d orbitals induces strong super-exchange interaction between in-plane Cu atoms.

Cubane 구조를 가진 Co₄ 분자자성체의 전자구조 및 자기구조계산

박기택(Key Taeck Park) 한국자기학회 2017 韓國磁氣學會誌 Vol.27 No.4

We have studied electronic and magnetic structure of cubane-type Co magnetic molecule using density functional method. The calculated density of states show Co<SUP>+2</SUP> ionic state and high-spin state because of large exchange interaction between inside Co 3d electrons. The exchange interaction J between Co atoms depends Co-O-Co angle. The calculated J is ferromagnetic with right angles. On the other hand J is antiferromagnetic with large angles since super-exchange interactions between Co<SUP>+2</SUP> atoms. It induces that Co cubane has a antiferromagnetic spin structure of AFM1 = [↑↑↓↓]

전이금속산화물 클러스터의 자기구조 및 자기이방성에너지 계산

박기택(Key Taeck Park) 한국자기학회 2011 韓國磁氣學會誌 Vol.21 No.1

We have studied magnetic structure and magnetic anisotropy energy of cubic transition metal mono-oxide cluster FeO and MnO using OpenMX method based on density functional method. The calculation results show that the antiferromagnetic spin arrangement has the lowest energy for FeO and MnO due to the superexchange interactions. The magnetic anisotropy is only found for antiferromagnetically ordered FeO cluster, since occupied electron of 3d down-spin level induces the spin-orbit couplings with 〈111〉 directed angular momentum.

Mn-dimer 분자자성체의 전자구조 및 자기구조 계산

박기택(Key Taeck Park) 한국자기학회 2014 韓國磁氣學會誌 Vol.24 No.4

We have studied electronic and magnetic structure of Mn-dimer molecule using OpenMX method based on density functional method. The calculated density of states shows that the four O atoms split e<SUB>g</SUB> and t<SUB>2g</SUB> energy levels. The energy splitting by the crystal field is smaller than bulk MnO with cubic structure, because of small coordination number of atoms. Total energy with antiferromagnetic spin configuration is lower than that of ferromagnetic configurations. Calculated exchange interaction J between Mn atoms is one order larger than that of the other Mn-O magnetic molecules. That comes from the direct exchange interaction between Mn 3d orbitals and the super-exchange interactions caused by strong σ-bonding of Mn-O orbitals.

이차원 전이금속 산화물 분자자성체의 자기이방성

박기택(Key Taeck Park) 한국자기학회 2019 韓國磁氣學會誌 Vol.29 No.1

We investigated the magnetic anisotropy energy of 2-dimensional transition-metal (TM= Fe,Co,Ni) oxide molecular magnet using 1st principle density functional method with spin-orbit interaction. The calculation results show that the magnetic easy-axis is along the line between TM and TM atoms and the hard-axis is perpendicular to the TMO plane except NiO. Partial electron occupation of d<SUB>yz</SUB> orbital induce the unquenched orbital momentum and LS coupling. It makes the easy-axis and hard-axis along x and z direction, respectively. For TMO, FeCoO₂ represents the largest anisotropy energy because of nearly half filled d<SUB>yz</SUB> orbital.