Kyung Hee University · 材料科学
Professor Hyun-Joo Koo's research lab specializes in theoretical and computational quantum chemistry, focusing on the electronic and magnetic properties of complex oxides. The lab employs first-principles density functional theory (DFT) and tight-binding calculations to unravel spin-lattice models in low-dimensional magnetic materials, particularly those exhibiting spin gaps, geometric frustration, and unconventional magnetic ordering. Key research directions include understanding the role of super-superexchange interactions, O-M-O bridges (M = V⁵⁺, Mo⁶⁺, Sb⁵⁺, Te⁴⁺), and spin-orbital coupling in determining magnetic behavior in layered and chain-based oxides. The lab also investigates the interplay between electronic structure, crystal symmetry, and magnetic dimensionality in materials such as pyrophosphates, wolframites, and copper-based oxides.
Figures are computed from collected data and may differ slightly.
Large transparent blue crystals of vanadyl pyrophosphate, (VO)(2)P(2)O(7), were grown from a phosphorus pentoxide flux, and the single-crystal X-ray structure of (VO)(2)P(2)O(7) was determined with high precision. On the basis of spin dimer analysis, we examined the spin exchange interactions of (VO)(2)P(2)O(7) and its precursor VO(HPO(4)).0.5H(2)O. Our analysis of (VO)(2)P(2)O(7) using two high-precision crystal structures shows unambiguously that the V3-V4 chain has a larger spin gap than does
The spin lattice model for the spin-gapped layered magnetic solids Na3Cu2SbO6 and Na2Cu2TeO6 was examined by evaluating the three spin exchange interactions of their Cu2MO6 (M = Sb, Te) layers in terms of spin dimer analysis based on extended Hückel tight binding calculations and mapping analysis based on first principles density functional theory electronic band structure calculations. For both compounds, our calculations show that the two strongest spin exchange interactions, that is, the Cu-O
First-principles density functional theory calculations show that the spin-lattice of Sr(3)Fe(2)O(5) is practically 2D in terms of its spin-exchange interactions. The magnetic dipole-dipole interactions are found to be essential for the 3D magnetic ordering of Sr(3)Fe(2)O(5) at a very low temperature.
The quaternary magnetic oxide Bi4Cu3V2O14 consists of Cu4O8 triple chains made up of corner-sharing CuO4 square planes. To determine its spin-lattice, the spin exchange interactions of Bi4Cu3V2O14 were evaluated by performing a spin dimer analysis based on tight-binding calculations and a mapping analysis based on first principles density functional theory calculations. Both calculations show that the spin-lattice of Bi4Cu3V2O14 is not an antiferromagnetically coupled diamond chain, which result
The distorted wolframite-type oxides CuWO4 and CuMoO4-III have a structure in which CuO4 zigzag chains, made up of cis-edge-sharing CuO6 octahedra, run along the c-direction and hence exhibit low-dimensional magnetic properties. We examined the magnetic structures of these compounds and their isostructural analogue Cu(Mo(0.25)W0.75)O4 on the basis of the spin-orbital interaction energies calculated for their spin dimers. Our study shows that these compounds consist of two-dimensional (2D) magnet
The spin-lattice models relevant for the magnetic oxides Rb2Cu2(MoO4)3, BaCu2V2O8, and KBa3Ca4Cu3V7O28 were determined by evaluating the relative strengths of the spin-exchange interactions between their Cu2+ ions on the basis of spin dimer analysis. Our study shows that the O-M-O bridges (M = V5+, Mo6+) between the magnetic ions Cu2+, provided by the MO4 tetrahedra, are crucial for the spin-exchange interactions and hence for deducing the spin-lattice models needed to interpret the magnetic pro
The spin-1/2 Cu2+ ions of LiCuVO4 form one-dimensional chains along the b direction, and the spin frustration in LiCuVO4 is described in terms of the nearest-neighbor ferromagnetic exchange J1 and the next-nearest-neighbor antiferromagnetic exchange J2 in these chains. Recently, it has become controversial whether or not J1 is stronger in magnitude than J2. To resolve this controversy, we determined the crystal structure of LiCuVO4 at 1.6 K by neutron diffraction, analyzed the magnetic susceptib
The spin exchange interactions of the magnetic oxides Ba3Cr2O8, Ba3Mn2O8, Na4FeO4, and Ba2CoO4 with a three-dimensional network of isolated MO4 (M = Cr, Mn, Fe, Co) tetrahedra were examined by performing spin dimer analysis on the basis of tight-binding electronic structure calculations. Although the shortest O...O distances between adjacent MO4 tetrahedra are longer than the van der Waals distance, our analysis shows that the super-superexchange interactions between adjacent MO4 tetrahedra are
In cupric oxide CuO, each Cu(2+) ion has 12 nearest-neighbor Cu(2+) ions grouped into six pairs related by inversion symmetry. The relative strengths of the Cu-O-Cu superexchange interactions in cupric oxide CuO were estimated by spin dimer analysis to confirm that the strongest superexchange interactions form one-dimensional antiferromagnetic chains along the [101] direction, and the remaining interactions are weak. We analyzed ordered arrangements of these one-dimensional antiferromagnetic cha
The CrVO(4)-type magnetic oxides MM'O(4) consist of edge-sharing MO(4) octahedral chains condensed with M'O(4) tetrahedra and exhibit a wide variety of magnetic structures. The magnetic properties of these oxides were examined by studying their spin exchange interactions on the basis of spin dimer analysis. The nature and magnitudes of the intra- and interchain spin exchange interactions depend on the square-to-rectangle distortion in the basal planes of the MO(4) chain and on the difference bet
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