@article{koo_chang_velev_2010, title={Ion-current diode with aqueous Gel/SiO2 nanofilm interfaces}, volume={6}, number={13}, journal={Small (Weinheim An Der Bergstrasse, Germany)}, author={Koo, H. J. and Chang, S. T. and Velev, O. D.}, year={2010}, pages={1393–1397} } @article{koo_whangbo_2006, title={Importance of the O-M-O bridges (M = V5+, Mo6+) for the spin-exchange interactions in the magnetic oxides of Cu2+ ions bridged by MO4 tetrahedra: Spin-lattice models of Rb2Cu2(MoO4)(3), BaCu2V2O8, and KBa3Ca4Cu3V7O28}, volume={45}, ISSN={["1520-510X"]}, DOI={10.1021/ic060392w}, abstractNote={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 properties of these oxides. The spin-lattice model of Rb2Cu2(MoO4)3 is not a uniform chain but two interpenetrating spin ladders that interact weakly with geometric spin frustration. The spin-lattice model of BaCu2V2O8 is an alternating chain as expected, but the spin-exchange paths responsible for it differ from those expected. With respect to the strongest spin exchange of BaCu2V2O8, the spin exchange of KBa3Ca4Cu3V7O28 is only slightly weaker, but the strongest spin exchange of Rb2Cu2(MoO4)3 is much weaker. This difference in the spin-exchange strengths is caused by the difference in the bridging modes of the MO4 tetrahedra leading to these spin-exchange interactions.}, number={11}, journal={INORGANIC CHEMISTRY}, author={Koo, Hyun-Joo and Whangbo, Myung-Hwan}, year={2006}, month={May}, pages={4440–4447} } @article{koo_dai_whangbo_2005, title={Importance of supersuperexchange interactions in determining the dimensionality of magnetic properties. Determination of strongly interacting spin exchange paths in A(2)CU(PO4)(2) (A = Ba, Sr), ACuP(2)O(7) (Ba, Ca, Sr, Pb), CaCuGe2O6, and Cu2UO2(PO4)(2) on the basis of qualitative spin dimer analysis}, volume={44}, ISSN={["1520-510X"]}, DOI={10.1021/ic050159i}, abstractNote={The patterns of the Cu(2+) ion arrangements in the magnetic oxides A(2)Cu(PO(4))(2) (A = Ba, Sr), ACuP(2)O(7) (Ba, Ca, Sr, Pb), CaCuGe(2)O(6), and Cu(2)UO(2)(PO(4))(2) are quite different from the patterns of the strongly interacting spin exchange paths deduced from their magnetic properties. This apparently puzzling observation was explained by evaluating the strengths of the Cu-O-Cu superexchange and Cu-O...O-Cu supersuperexchange interactions of these oxides on the basis of qualitative spin dimer analysis. Supersuperexchange interactions are found to be crucial in determining the dimensionality of magnetic properties of these magnetic oxides.}, number={12}, journal={INORGANIC CHEMISTRY}, author={Koo, HJ and Dai, D and Whangbo, MH}, year={2005}, month={Jun}, pages={4359–4365} } @article{woodward_choi_musfeldt_haraldsen_wei_koo_dai_whangbo_landee_turnbull_2005, title={Understanding the color properties of (C5H9NH3)(2)CuBr4 in high magnetic fields}, volume={71}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.71.174416}, abstractNote={We report the optical and magneto-optical properties of ${({\mathrm{C}}_{5}{\mathrm{H}}_{9}\mathrm{N}{\mathrm{H}}_{3})}_{2}\mathrm{Cu}{\mathrm{Br}}_{4}$, an $S=1∕2$ low-dimensional molecular antiferromagnet. Complementary electronic structure calculations demonstrate that the color properties of this material are dominated by excitations of the $\mathrm{Cu}{\mathrm{Br}}_{4}^{2\ensuremath{-}}$ chromophore. In an applied magnetic field, ${({\mathrm{C}}_{5}{\mathrm{H}}_{9}\mathrm{N}{\mathrm{H}}_{3})}_{2}\mathrm{Cu}{\mathrm{Br}}_{4}$ displays a rich magnetochromic response that is particularly strong in the direction of the bromide-bromide bridge pairs between the chains. This effect is attributed to a field-induced reorientation of the $\mathrm{Cu}{\mathrm{Br}}_{4}^{2\ensuremath{-}}$ anions. These color changes are correlated with critical fields in the magnetization.}, number={17}, journal={PHYSICAL REVIEW B}, author={Woodward, JD and Choi, J and Musfeldt, JL and Haraldsen, JT and Wei, X and Koo, HJ and Dai, D and Whangbo, MH and Landee, CP and Turnbull, MM}, year={2005}, month={May} } @article{rocquefelte_goubin_koo_whangbo_jobic_2004, title={Investigation of the origin of the empirical relationship between refractive index and density on the basis of first principles calculations for the refractive indices of various TiO2 phases}, volume={43}, ISSN={["1520-510X"]}, DOI={10.1021/ic035383r}, abstractNote={On the basis of first principles electronic structure calculations, we determined the dielectric functions, the refractive indices, and the extinction coefficients of the seven different phases of TiO(2) and then examined why the refractive index is related to the density by the empirical Glastone-Dale equation. The zero frequency limit of the refractive index, n(0), is found to be a good approximation for the refractive index n determined around 2 eV. Our study indicates that the major factor influencing n in a series of closely related systems is the structure compactness. This finding suggests a way of preparing new UV absorbers with low refractive index.}, number={7}, journal={INORGANIC CHEMISTRY}, author={Rocquefelte, X and Goubin, F and Koo, HJ and Whangbo, MH and Jobic, S}, year={2004}, month={Apr}, pages={2246–2251} } @article{whangbo_dai_koo_2004, title={Spin dimer and classical spin analyses of the ordered magnetic structures of alkali iron pyrophosphates NaFeP2O7 and LiFeP2O7}, number={19}, journal={Dalton Transactions (Cambridge, England : 2003)}, author={Whangbo, M. H. and Dai, D. and Koo, H. J.}, year={2004}, pages={3019–3025} } @article{whangbo_koo_dai_villesuzanne_2003, title={A discussion on the apparently puzzling structural, electrical and magnetic properties of BaVS3}, volume={175}, ISSN={["0022-4596"]}, DOI={10.1016/S0022-4596(03)00346-3}, abstractNote={The ternary vanadium sulfide BaVS3 consists of VS3 chains made up of face sharing VS6 octahedra, and exhibits a number of structural, electrical and magnetic properties that are not explained in terms of the normal metallic state. Our analysis indicates that the spin ordering of BaVS3 taking place below 30 K is most probably random along the chain direction. Thus the puzzling properties of BaVS3 are explained in terms of the broken-symmetry electronic state in which pairs of nonmagnetic V atoms alternate with those of magnetic V atoms in each VS3 chain. The origin of this broken-symmetry state was discussed on the basis of cooperative Jahn–Teller distortion and lattice strain.}, number={2}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Whangbo, MH and Koo, HJ and Dai, D and Villesuzanne, A}, year={2003}, month={Nov}, pages={384–388} } @article{dai_koo_whangbo_2003, title={Analysis of the spin exchange interactions of ferromagnetic CdVO3 in terms of first principles and qualitative electronic structure calculations}, volume={175}, ISSN={["0022-4596"]}, DOI={10.1016/S0022-4596(03)00307-4}, abstractNote={First principles spin-polarized electronic band structure calculations were carried out for three ordered spin states of CdVO3, and the strengths of its corner- and edge-sharing spin exchange interactions were estimated. To gain insight into why CdVO3 exhibits ferromagnetism while CaV2O5 does not despite their apparent structural similarity, the spin exchange interactions of CdVO3 and CaV2O5 were compared in terms of spin dimer analysis using extended Hückel tight binding calculations, and the local geometries of their V4+ ions were examined.}, number={2}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Dai, D and Koo, HJ and Whangbo, MH}, year={2003}, month={Nov}, pages={341–347} } @article{soulard_rocquefelte_jobic_dai_koo_whangbo_2003, title={Metal-ligand bonding and rutile- versus CdI2-type structural preference in platinum dioxide and titanium dioxide}, volume={175}, ISSN={["0022-4596"]}, DOI={10.1016/S0022-4596(03)00323-2}, abstractNote={First principles electronic structure calculations were carried out to determine the relative stabilities of the rutile- and CdI2-type structures of platinum dioxide (PtO2) and titanium dioxide (TiO2). The orbital interactions between the transition metal d- and oxygen p-orbitals were analyzed to gain insight into why PtO2 has both the rutile- and CdI2-type structures, but TiO2 has only the rutile-type structure. The cause for the large difference in the c/a ratios of the CdI2-type structures of TiO2 and PtO2 was examined.}, number={2}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Soulard, C and Rocquefelte, X and Jobic, S and Dai, D and Koo, HJ and Whangbo, MH}, year={2003}, month={Nov}, pages={353–358} } @article{koo_seo_whangbo_2001, title={Consequence of the metal-atom clustering on the magnetic properties in vanadium sulfide V5S8}, volume={160}, ISSN={["1095-726X"]}, DOI={10.1006/jssc.2001.9260}, abstractNote={Abstract On the basis of qualitative bonding considerations and tight-binding electronic band structure calculations, we examined how the unequal spin moment distribution is related to the metal-atom clustering in V 5 S 8 and why V 5 S 8 exhibits both localized and itinerant magnetic properties.}, number={1}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Koo, HJ and Seo, DK and Whangbo, MH}, year={2001}, month={Aug}, pages={287–291} } @article{schlueter_ward_geiser_wang_kini_parakka_morales_koo_whangbo_winter_et al._2001, title={Crystal structure, physical properties and electronic structure of a new organic conductor beta ''-(BEDT-TTF)(2)SF5CHFCF2SO3}, volume={11}, ISSN={["0959-9428"]}, DOI={10.1039/b008735l}, abstractNote={John A. Schlueter,* Brian H. Ward, Urs Geiser, Hau H. Wang, Aravinda M. Kini, James Parakka, Emilio Morales, H.-J. Koo, M.-H. Whangbo, R. W. Winter, J. Mohtasham and Gary L. Gard Materials Science Division, Argonne National Laboratory, Argonne IL 60439. E-mail: JASchlueter@anl.gov Department of Chemistry, North Carolina State University, Raleigh, USA NC 27695-8204 Department of Chemistry, Portland State University, Portland, USA OR 97207-0751}, number={8}, journal={JOURNAL OF MATERIALS CHEMISTRY}, author={Schlueter, JA and Ward, BH and Geiser, U and Wang, HH and Kini, AM and Parakka, J and Morales, E and Koo, HJ and Whangbo, MH and Winter, RW and et al.}, year={2001}, pages={2008–2013} } @article{jung_koo_dai_whangbo_2001, title={Electronic structure study of scanning tunneling microscopy images of the rutile TiO2(110) surface and their implications on the surface relaxation}, volume={473}, ISSN={["1879-2758"]}, DOI={10.1016/S0039-6028(00)00970-5}, abstractNote={In scanning tunneling microscopy (STM) images recorded for rutile TiO2(1 1 0) surfaces with oxygen vacancies, the non-defect-site five-coordinate Ti atoms and the vacancy sites of the bridging oxygen atom rows appear bright while the six-coordinate Ti atoms and the bridging oxygen atoms appear dark. To find what kinds of surface relaxation can cause such STM images, we carried out partial density plot calculations for the unrelaxed structure and a number of model relaxed structures of the rutile TiO2(1 1 0) surface with oxygen vacancies using the extended Hückel tight binding method. We also performed density functional theory calculations to estimate the Ti atom displacements for the three types of Ti atoms present on TiO2(1 1 0) surfaces with oxygen vacancies.}, number={3}, journal={SURFACE SCIENCE}, author={Jung, D and Koo, HJ and Dai, D and Whangbo, MH}, year={2001}, month={Feb}, pages={193–202} } @article{rudko_long_musfeldt_koo_whangbo_revcolevschi_dhalenne_bernholdt_2001, title={Electronic transitions in doped and undoped copper germanate}, volume={13}, ISSN={["0897-4756"]}, DOI={10.1021/cm000703f}, abstractNote={We report an analysis of the absorption edge anisotropy in CuGeO3 based on a comparison of polarized optical data with electronic structure calculations in the framework of the extended Huckel tight binding model. Taking the z axis as parallel to the CuO4 chains, we ascribe the absorption edge in the magnetic chain direction to O 2px, 2py → singly filled Cu 3d transitions and the edge in the transverse direction to O 2pz → singly filled Cu 3d excitations. The dual slope in the transverse direction is a direct consequence of the double maximum in the O 2pz density of states. The influence of Zn and Si doping on the electronic spectra of CuGeO3 is analyzed as well. Whereas neither impurity affects the phonon-assisted d−d band, Si doping smears the charge-transfer gap. This smearing of the gap by interchain impurity substitution is attributed to random distortions of the crystalline lattice giving rise to structurally induced changes in the electronic properties.}, number={3}, journal={CHEMISTRY OF MATERIALS}, author={Rudko, GY and Long, VC and Musfeldt, JL and Koo, HJ and Whangbo, MH and Revcolevschi, A and Dhalenne, G and Bernholdt, DE}, year={2001}, month={Mar}, pages={939–944} } @article{koo_whangbo_2001, title={Examination of the anisotropic spin exchange interactions of CuM2O6 (M = Sb, V, Nb) by spin dimer analysis}, volume={156}, ISSN={["0022-4596"]}, DOI={10.1006/jssc.2000.8969}, abstractNote={Abstract The anisotropic spin exchange interactions of the magnetic solids Cu M 2 O 6 ( M =Sb, V, Nb) were explained by analyzing their reported crystal structures and calculating the spin orbital interaction energies of their spin dimers. The magnetic orbital of each Cu 2+ site in Cu M 2 O 6 is given by the “ x 2 – y 2 ” orbital so that the magnitude of an antiferromagnetic spin exchange interaction for a given spin dimer increases when the arrangement of the nearest-neighbor square-planar CuO 4 units containing the magnetic orbitals provides a good sigma overlap between the adjacent magnetic orbitals. The one-dimensional magnetic chains of α -CuV 2 O 6 , β -CuNb 2 O 6 , and α -CuNb 2 O 6 run along a direction different than their edge-sharing CuO 4 chain directions. Our study predicts that the antiferromagnetic ordering in β -CuNb 2 O 6 should make the magnetic unit cell double the chemical unit cell along the b -direction.}, number={1}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Koo, HJ and Whangbo, MH}, year={2001}, month={Jan}, pages={110–116} } @article{pigos_jones_zhu_musfeldt_homes_koo_whangbo_schlueter_ward_wang_et al._2001, title={Infrared and optical properties of beta '-(ET)(2)SF5CF2SO3: Evidence for a 45 K spin peierls transition}, volume={13}, ISSN={["0897-4756"]}, DOI={10.1021/cm000839d}, abstractNote={We measured the polarized infrared reflectance of β‘-(ET)2SF5CF2SO3 as a function of temperature and analyzed the spin-exchange interactions of this salt by calculating the spin−orbital interaction energies between adjacent spin sites. The observed changes in vibrational properties below the 45 K transition support a weak lattice distortion in combination with a spin gap in this material. The spin-exchange interaction is predicted to occur primarily along the (−a +b) diagonal direction, in good agreement with the spectral data. In addition, notable frequency shifts of vibrational modes point to a second transition between 100 and 200 K. The low-lying electronic excitation in the stack direction (assigned as a charge-transfer feature based upon our electronic band structure calculations) shows distinct changes with temperature that are consistent with trends in the vibrational spectrum. The pattern of a high-temperature transition preceding the spin-Peierls transition is discussed in relation to other low-...}, number={4}, journal={CHEMISTRY OF MATERIALS}, author={Pigos, JM and Jones, BR and Zhu, ZT and Musfeldt, JL and Homes, CC and Koo, HJ and Whangbo, MH and Schlueter, JA and Ward, BH and Wang, HH and et al.}, year={2001}, month={Apr}, pages={1326–1333} } @article{manson_huang_lynn_koo_whangbo_bateman_otsuka_wada_argyriou_miller_2001, title={Long-range magnetic order in Mn[N(CN)(2)](2)(pyz) {pyz =pyrazine} susceptibility, magnetization, specific heat, and neutron diffraction measurements and electronic structure calculations}, volume={123}, DOI={10.1021/ja0024791}, abstractNote={Using dc magnetization, ac susceptibility, specific heat, and neutron diffraction, we have studied the magnetic properties of Mn[N(CN)2]2(pyz) (pyz = pyrazine) in detail. The material crystallizes in the monoclinic space group P2(1)/n with a = 7.3248(2), b = 16.7369(4), and c = 8.7905 (2) A, beta = 89.596 (2) degrees, V = 1077.65(7) A(3), and Z = 4, as determined by Rietveld refinement of neutron powder diffraction data at 1.35 K. The 5 K neutron powder diffraction data reflect very little variation in the crystal structure. Interpenetrating ReO3-like networks are formed from axially elongated Mn(2+) octahedra and edges made up of mu-bonded [N(CN)2](-) anions and neutral pyz ligands. A three-dimensional antiferromagnetic ordering occurs below T(N) = 2.53(2) K. The magnetic unit cell is double the nuclear one along the a- and c-axes, giving the (1/2, 0, 1/2) superstructure. The crystallographic and antiferromagnetic structures are commensurate and consist of collinear Mn(2+) moments, each with a magnitude of 4.15(6) mu(B) aligned parallel to the a-direction (Mn-pyz-Mn chains). Electronic structure calculations indicate that the exchange interaction is much stronger along the Mn-pyz-Mn chain axis than along the Mn-NCNCN-Mn axes by a factor of approximately 40, giving rise to a predominantly one-dimensional magnetic system. Thus, the variable-temperature magnetic susceptibility data are well described by a Heisenberg antiferromagnetic chain model, giving g = 2.01(1) and J/k(B) = -0.27(1) K. Owing to single-ion anisotropy of the Mn(2+) ion, field-induced phenomena ascribed to spin-flop and paramagnetic transitions are observed at 0.43 and 2.83 T, respectively.}, number={1}, journal={Journal of the American Chemical Society}, author={Manson, J. L. and Huang, Q. Z. and Lynn, J. W. and Koo, H. J. and Whangbo, M. H. and Bateman, R. and Otsuka, T. and Wada, N. and Argyriou, D. N. and Miller, J. S.}, year={2001}, pages={162–172} } @article{gourdon_evain_jobic_brec_koo_whangbo_corraze_chauvet_2001, title={On the origin of the root 7 x root 7 superstructure and the anomalous magnetic and transport properties of the layered compound Sr6V9S22O2}, volume={40}, ISSN={["0020-1669"]}, DOI={10.1021/ic001434y}, abstractNote={We examined why the 1T-VS2 layer of the layered compound Sr6V9S22O2 has the × superstructure in terms of electronic band structure calculations and metal−metal bonding across the shared edges of adjacent VS6 octahedra. On the basis of this analysis we explored how the anomalous magnetic and transport properties of Sr6V9S22O2 can be explained. Our work shows that the × superstructure is not caused by a charge density wave instability associated with Fermi surface nesting but by the metal−metal bonding through the shared edges of adjacent VS6 octahedra. The weak and strong electron localizations observed for Sr6V9S22O2 were discussed in terms of three-center two-electron and two-center two-electron V−V bonds in the 1T-VS2 layers.}, number={12}, journal={INORGANIC CHEMISTRY}, author={Gourdon, O and Evain, M and Jobic, S and Brec, R and Koo, HJ and Whangbo, MH and Corraze, B and Chauvet, O}, year={2001}, month={Jun}, pages={2898–2904} } @article{koo_whangbo_coste_jobic_2001, title={Spin dimer analysis for antiferromagnetic spin exchange interactions of magnetic solids with several unpaired electrons per spin site: Trends in the spin exchange parameters of the compounds consisting of MnF5 chains and CrX2 (X = O, S) layers}, volume={156}, ISSN={["1095-726X"]}, DOI={10.1006/jssc.2000.9025}, abstractNote={Abstract For magnetic solids with several unpaired spins per spin site, the average spin orbital interaction energies 〈Δ e 〉 and the average spin orbital interaction energy squares 〈(Δ e ) 2 〉 were defined as a qualitative measure for the strengths of their antiferromagnetic spin exchange interactions. The trends in the antiferromagnetic spin exchange interactions of the magnetic solids containing MnF 5 chains and Cr X 2 ( X =O, S) layers were examined in terms of the 〈Δ e 〉 and 〈(Δ e ) 2 〉 values calculated for their spin dimers.}, number={2}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Koo, HJ and Whangbo, MH and Coste, S and Jobic, S}, year={2001}, month={Feb}, pages={464–469} } @article{koo_whangbo_2001, title={Spin dimer analysis of the anisotropic spin exchange interactions in the distorted wolframite-type oxides CuWO4, CuMoO4-III, and Cu(Mo0.25W0.(75))O-4}, volume={40}, ISSN={["0020-1669"]}, DOI={10.1021/ic001445r}, abstractNote={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) magnetic sheets defined by one superexchange (intrachain Cu-O-Cu) and three super-superexchange (interchain Cu-O.O-Cu) paths, the strongly interacting spin units of these 2D magnetic sheets are the two-leg antiferromagnetic (AFM) ladder chains running along the (a + c)-direction, and the spin arrangement between adjacent AFM ladder chains leads to spin frustration. The similarities and differences in the magnetic structures of CuWO4, CuMoO4-III, and Cu(Mo(0.25)W0.75)O4 were discussed by examining how adjacent AFM ladder chains are coupled via the superexchange paths in the 2D magnetic sheets and how adjacent 2D magnetic sheets are coupled via another superexchange paths along the c-direction. Our study reproduces the experimental finding that the magnetic unit cell is doubled along the a-axis in CuWO(4) and along the c-axis in CuMoO4-III and predicts that the magnetic unit cell should be doubled along the a- and b-axes in Cu(Mo(0.25)W0.75)O4. In the understanding of the strength of a super-superexchange interaction, the importance of the geometrical factors controlling the overlap between the tails of magnetic orbitals was pointed out.}, number={9}, journal={INORGANIC CHEMISTRY}, author={Koo, HJ and Whangbo, MH}, year={2001}, month={Apr}, pages={2161–2169} } @article{whangbo_koo_2001, title={Structural and electronic features of BaIrO3 causing the simultaneous occurrence of weak ferromagnetism and charge density wave formation}, volume={118}, ISSN={["0038-1098"]}, DOI={10.1016/S0038-1098(01)00166-1}, abstractNote={The ferromagnetic transition of BaIrO3 at 175 K is accompanied by charge density wave formation [Solid State Commun. 113 (2000) 657]. We examined the probable cause for this observation on the basis of tight-binding band electronic structure calculations for BaIrO3. In support of the experimental observation, our calculations show that BaIrO3 should be regarded as a weakly localized metal above 175 K, its t2g-block band density of states has a sharp peak at the Fermi level, and its Fermi surfaces have partially nested pieces.}, number={10}, journal={SOLID STATE COMMUNICATIONS}, author={Whangbo, MH and Koo, HJ}, year={2001}, pages={491–495} } @article{jobic_brec_pasturel_koo_whangbo_2001, title={Theoretical study of possible iridium ditelluride phases attainable under high pressure}, volume={162}, DOI={10.1006/jssc.2001.9341}, abstractNote={Abstract We examined the feasibility of preparing new high-pressure polymorphs of IrTe2 by determining the relative energies and unit cell volumes of known and hypothetical forms of IrTe2 on the basis of first-principles electronic band structure calculations using the Vienna ab initio simulation package (VASP). The IrTe2 polymorphs included in our analysis are three known phases, i.e., the polymeric CdI2-type, pyrite-type, and monoclinic IrTe2 phases, as well as four hypothetical phases, i.e., ramsdelite-type, pyrolusite-type, IrS2-type, and marcasite-type phases. The charge balances of these IrTe2 phases were analyzed by carrying out extended Huckel tight-binding electronic band structure calculations for the crystal structures optimized by VASP calculations.}, number={1}, journal={Journal of Solid State Chemistry}, author={Jobic, S. and Brec, R. and Pasturel, A. and Koo, H. J. and Whangbo, M. H.}, year={2001}, pages={63–68} } @article{koo_suh_woo_2001, title={Variance tolerancing and decomposition in short-staple spinning processes Part I: Modeling spun yarn strength through intrinsic components}, volume={71}, DOI={10.1177/004051750107100101}, abstractNote={ A variance tolerancing method is developed as a means for separating and estimating random errors associated with raw materials and yarn structures from process-induced errors based on structural relationships governing the strength of a spun yarn. The method is successfully used to estimate the mean and variance of spun yarn strength by propagating the statistical parameters of fiber properties onto those of the resulting spun yarns. In developing the new estimation procedure, probabilistic models based on the distributions of fiber length and tensile properties are combined with geometric and structural models of fiber arrangements in spun yarns. For the first time, the concept of “effective gauge length” is used to model and simulate the breakage process of spun yarns. The new concept and specific methodology are aimed at better controlling process and product characteristics by quantifying the variances according to their sources. }, number={1}, journal={Textile Research Journal}, author={Koo, H. J. and Suh, M. W. and Woo, J. L.}, year={2001}, pages={1–7} } @article{suh_koo_woo_2001, title={Variance tolerancing and decomposition in short-staple spinning processes part II: Simulations and applications to ring and OE spun yarns}, volume={71}, ISSN={["0040-5175"]}, DOI={10.1177/004051750107100203}, abstractNote={ The variance tolerancing and decomposition method developed in Part I of this paper is applied to a large amount of fiber and yarn test data obtained from a spinning mill during a three-year period. The variabilities of single-end strengths found in six different ring spun and open-end yarns are successfully decomposed into random and processinduced variance components by tolerancing the variances of the matching fiber length and tensile properties. A total of 43,080 single-end yarn strength tests, 4,200,000 AFIS® fiber lengths, and over 70,000 Mantis® single-fiber tensile tests are performed for the required parameter estimation, simulation, and model validation. The results confirm that variance tolerancing through “effective gauge length” and other intrinsic components is effective for variance estimation and decomposition. Most significant is that the processinduced variances account for 69-82% of the total yarn strength variations, signifying the importance of and challenges in controlling and reducing process variances in spun yarn manufacturing. }, number={2}, journal={TEXTILE RESEARCH JOURNAL}, author={Suh, MW and Koo, HJ and Woo, JL}, year={2001}, month={Feb}, pages={105–111} } @article{whangbo_koo_lee_2000, title={Analysis of nearest-neighbor spin exchange interactions by molecular orbital calculations: anisotropic spin exchange interactions in MV3O7 (M = Cd, Ca, Sr) and alpha '-NaV2O5}, volume={114}, DOI={10.1016/s0038-1098(99)00571-2}, abstractNote={Spin-dimer analysis was carried out for the room temperature structures of MV3O7 (M=Cd, Ca, Sr) and the 15 K structure of α′-NaV2O5 reported by Lüdecke et al. to examine the relative magnitudes of the nearest-neighbor spin exchange interactions between their unpaired spins. Our analysis explains why the magnetic susceptibility of the stripe spin structure of MV3O7 (M=Cd, Ca, Sr) exhibits a one-dimensional spin-1/2 Heisenberg chain-like behavior. Our study indicates that the 15 K crystal structure of α′-NaV2O5 is likely to have a spin gap and exhibit spin frustration. The predicted spin frustration is not consistent with the singlet ground state expected for a spin-Peierls system.}, number={1}, journal={Solid State Communications}, author={Whangbo, M. H. and Koo, H. J. and Lee, K. S.}, year={2000}, pages={27–32} } @article{koo_whangbo_2000, title={Analysis of the spin exchange interactions in the extended magnetic solids K2NiF4, K2CuF4, La2CuO4, Nd2CuO4, KNiF3, and KCuF3}, volume={151}, ISSN={["1095-726X"]}, DOI={10.1006/jssc.2000.8627}, abstractNote={Abstract The spin exchange parameters J of the extended magnetic solids K2NiF4, K2CuF4, La2CuO4, Nd2CuO4, KNiF3, and KCuF3 were analyzed by examining the structures of their spin monomers and calculating the energy differences Δe in the spin levels of their spin dimers. The trends in the observed J parameters are well explained in terms of the Δe values obtained from extended Huckel molecular orbital calculations. The Δe value of a spin dimer is related only to the antiferromagnetic component of its J, but the spin dimer analysis based on Δe allows one to correlate the nature of the magnetic interaction with the structure of the spin dimer.}, number={1}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Koo, HJ and Whangbo, MH}, year={2000}, month={Apr}, pages={96–101} } @article{koo_whangbo_2000, title={Analysis of the spin exchange interactions in the three phases of vanadium pyrophosphate, (VO)(2)P2O7, in terms of spin-orbital interaction energy}, volume={39}, ISSN={["0020-1669"]}, DOI={10.1021/ic000046t}, abstractNote={The spin exchange interactions in the ambient-pressure orthorhombic (APO), high-pressure orthorhombic (HPO), and ambient-pressure monoclinic (APM) phases of the vanadium pyrophosphate, (VO)2P2O7, were analyzed by calculating the spin-orbital interaction energies delta e-delta e0 of their spin dimers. The anisotropy of the spin exchange interactions in the HPO phase is well explained by the delta e-delta e0 values. For the APO phase, the reported crystal structure does not provide accurate enough delta e-delta e0 values to conclude unambiguously which of the V1-V2 and V3-V4 chains has a larger spin gap and which of the bridged and edge-sharing spin dimers has a stronger spin exchange interaction in the V1-V2 and V3-V4 chains. The APM phase is predicted to exhibit essentially two spin gaps, with a large spin gap for the V8-V5-V7-V6 chain and a very small one for the V4-V2-V3-V1 chain.}, number={16}, journal={INORGANIC CHEMISTRY}, author={Koo, HJ and Whangbo, MH}, year={2000}, month={Aug}, pages={3599–3604} } @article{koo_whangbo_picard_jobic_potel_gougeon_2000, title={Electronic band structure study of A(2)Mo(9)S(11) (A=K, Rb) and K1.8Mo9S11}, volume={155}, ISSN={["0022-4596"]}, DOI={10.1006/jssc.2000.8912}, abstractNote={Abstract The electronic band structures of A 2 Mo 9 S 11 ( A =K, Rb) and K 1.8 Mo 9 S 11 are examined by extended Huckel tight binding calculations. K 2 Mo 9 S 11 and K 1.8 Mo 9 S 11 are metallic and exhibit resistivity anomalies below ∼115 and ∼80 K, respectively. The origin of these anomalies is explained in terms of their Fermi surfaces. Our study indicates that the resistivity anomalies of these compounds are caused by the partial nesting of their two-dimensional Fermi surfaces and that both K 2 Mo 9 S 11 and Rb 2 Mo 9 S 11 should exhibit a charge density wave phenomenon.}, number={1}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Koo, HJ and Whangbo, MH and Picard, S and Jobic, S and Potel, M and Gougeon, P}, year={2000}, month={Nov}, pages={124–128} } @article{whangbo_koo_2000, title={Investigation of the spin exchange interactions in the nanotube system Na2V3O7 by spin dimer analysis}, volume={115}, ISSN={["1879-2766"]}, DOI={10.1016/S0038-1098(00)00258-1}, abstractNote={The relative magnitudes of the spin exchange interactions expected for the nanotubes of Na2V3O7 were examined by identifying the spin dimers of the nanotube and calculating their spin orbital interaction energies. Our analysis indicates that the spin exchange interactions of the nanotube are not described by three-legged ladders, but by six mutually intersecting helical chains, and the magnetic properties of the nanotube in the low temperature region can be well approximated by those of a single helical chain. Each helical chain is described by four antiferromagnetc spin exchange parameters J1–J4 with the repeat sequence [–J2–J1–J3–J4–]∞, where |J1|>|J2|>|J3|>|J4|. The nanotube is expected to have a spin gap.}, number={12}, journal={SOLID STATE COMMUNICATIONS}, author={Whangbo, MH and Koo, HJ}, year={2000}, pages={675–678} } @article{schiller_schmidt_balthes_schweitzer_koo_whangbo_heinen_klausa_kircher_strunz_2000, title={Investigations of the Fermi surface of a new organic metal: (BEDT-TTF)(4)[Ni(dto)(2)]}, volume={51}, ISSN={["0295-5075"]}, DOI={10.1209/epl/i2000-00329-2}, abstractNote={The Fermi surface (FS) of the new organic metal (BEDT-TTF)4[ Ni(dto)2] has been investigated by de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) experiments. In both quantum oscillations with two different frequencies Fα = 634 T and Fβ = 4245 T are observed. These results confirm the calculated FS, which consists of one-dimensional and two-dimensional parts separated by a small energy gap. It is shown that the temperature and field dependence of the oscillation amplitudes can be well described by standard Lifshitz-Kosevich theory considering the magnetic breakdown by the so-called coupled network model. Beatings of the oscillation amplitudes are observed by field-dependent dHvA and SdH experiments. They can be explained by a slightly warped FS showing that this material represents a quasi–two-dimensional electronic system. The observed beating nodes in the dHvA and SdH signals appear at different magnetic fields. This fact is discussed in terms of additional scattering mechanisms.}, number={1}, journal={EUROPHYSICS LETTERS}, author={Schiller, M and Schmidt, W and Balthes, E and Schweitzer, D and Koo, HJ and Whangbo, MH and Heinen, I and Klausa, T and Kircher, P and Strunz, W}, year={2000}, month={Jul}, pages={82–88} } @article{hagrman_laduca_koo_rarig_haushalter_whangbo_zubieta_2000, title={Ligand influences on the structures of molybdenum oxide networks}, volume={39}, DOI={10.1021/ic0004961}, number={19}, journal={Inorganic Chemistry}, author={Hagrman, P. J. and Laduca, R. L. and Koo, H. J. and Rarig, R. and Haushalter, R. C. and Whangbo, M. H. and Zubieta, J.}, year={2000}, pages={4311–4317} } @article{bartlett_essex_koo_nandhakumar_robertson_whangbo_2000, title={Molecular self-assembly on surfaces of organic conducting salts: Epitaxial monolayer films of naphthalene on the (001) surface of (TMTSF)(2)PF6}, volume={104}, ISSN={["1089-5647"]}, DOI={10.1021/jp000013z}, abstractNote={Pristine and naphthalene-adsorbed (001) surfaces of the organic conducting salt (TMTSF)(2)PF6 were examined by scanning tunneling microscopy (STM) to determine the structure of epitaxial monolayer films of naphthalene on the (001) surface. The observed STM images were interpreted by calculating partial electron density plots of the surface, and for naphthalene-adsorbed surfaces, by carrying out Monte Carlo simulations for the adsorption of a naphthalene molecule on the surface. The STM images recorded for the pristine (001) surface correspond to the cation layer of (TMTSF)2PF6, and each circular bright spot of the molecular-resolution STM images represents the three hydrogen atoms of the most protruding methyl group of a TMTSF molecule on the (001) surface. Naphthalene molecules adsorbed on this surface form a pseudomorphic (1 x 1) overlayer structure with respect to the underlying substrate. The naphthalene overlayer shows mechanical stability against etching by the scanning tip. An identical overlayer structure of naphthalene was obtained from several different preparation methods. On the cation-layer (001) surface naphthalene is adsorbed on each "four-methyl-step'' defined by four methyl groups of two adjacent TMTSF molecules within each TMTSF stack.}, number={31}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Bartlett, PN and Essex, JW and Koo, HJ and Nandhakumar, IS and Robertson, N and Whangbo, MH}, year={2000}, month={Aug}, pages={7394–7402} } @article{jones_olejniczak_dong_pigos_zhu_garlach_musfeldt_koo_whangbo_schlueter_et al._2000, title={Optical spectra and electronic band structure calculations of beta ''-(ET)(2)SF5RSO3 (R = CH2CF2, CHFCF2, and CHF): Changing electronic properties by chemical tuning of the counterion}, volume={12}, ISSN={["1520-5002"]}, DOI={10.1021/cm000349l}, abstractNote={We report the polarized infrared reflectance spectra, optical conductivity, and electronic band structure of metallic β‘ ‘-(ET)2SF5CHFSO3 and compare our results with those of the β‘ ‘-(ET)2SF5CH2CF2SO3 superconductor and the β‘ ‘-(ET)2SF5CHFCF2SO3 metal/insulator material. We discuss the electronic structure of these organic molecular solids in terms of band structure, many-body effects, and disorder. On the basis of spectral similarities between the superconductor and metallic salts and structural differences in the anion pocket of all three, we conclude that the unusual electronic excitations observed in the β‘ ‘-(ET)2SF5CHFCF2SO3 metal/insulator material are not caused by electron correlation but are due to disorder-related localization.}, number={8}, journal={CHEMISTRY OF MATERIALS}, author={Jones, BR and Olejniczak, I and Dong, J and Pigos, JM and Zhu, ZT and Garlach, AD and Musfeldt, JL and Koo, HJ and Whangbo, MH and Schlueter, JA and et al.}, year={2000}, month={Aug}, pages={2490–2495} } @article{whangbo_koo_2000, title={Origin of the spin gap in sodium vanadium bronze Na9V14O35}, volume={115}, ISSN={["1879-2766"]}, DOI={10.1016/S0038-1098(00)00159-9}, abstractNote={The cause for the spin gap of Na9V14O35 was examined by identifying its spin dimers, calculating their spin orbital interaction energies and then finding a model spin Hamiltonian appropriate for Na9V14O35. In essence, the spin exchange interactions in the V10O30 chains of Na9V14O35 are equivalent to those of the fused chain of 10-node rings, where each node represents a spin site and nearest-neighbor spin exchange interactions are antiferromagnetic. To a first approximation, the energy gap between the ground and first excited states of this fused chain is the same as that of a 10-node ring. In general, the fused chain of n-node rings with even n is expected to have a spin gap.}, number={3}, journal={SOLID STATE COMMUNICATIONS}, author={Whangbo, MH and Koo, HJ}, year={2000}, pages={115–119} } @article{koo_whangbo_2000, title={Spin dimer analysis of the spin exchange interactions of the vanadium oxides AV(4)O(9) (A = Ca, Sr, Cs-2, NH2(CH2)(4)NH2)}, volume={153}, ISSN={["0022-4596"]}, DOI={10.1006/jssc.2000.8753}, abstractNote={Abstract The spin exchange interactions of the vanadium oxides A V 4 O 9 ( A =Ca, Sr, Cs 2 , and NH 2 (CH 2 ) 4 NH 2 ) were examined by calculating the spin orbital interaction energies of their spin dimers based on the extended Huckel method. The temperature T max at which the magnetic susceptibility maximum occurs in A V 4 O 9 ( A =Ca, Sr, Cs 2 , and NH 2 (CH 2 ) 4 NH 2 ) shows a wide variation (from 30 to 600 K) and increases in the order [NH 2 (CH 2 ) 4 NH 2 ]V 4 O 9 4 O 9 2 V 4 O 9 . The susceptibility at T max increases in the opposite order, and the room temperature susceptibility of [NH 2 (CH 2 ) 4 NH 2 ]V 4 O 9 is about twice as high as the maximum susceptibility of CaV 4 O 9 . These observations were examined by estimating the magnetic excitation energies of the strongly interacting spin units of A V 4 O 9 .}, number={2}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Koo, HJ and Whangbo, MH}, year={2000}, month={Sep}, pages={263–269} } @article{jung_koo_whangbo_2000, title={Study of the 18-electron band gap and ferromagnetism in semi- Heusler compounds by nea-spin-polarized electronic band structure calculations}, volume={527}, number={2000 Aug. 4}, journal={Journal of Molecular Structure [including Theochem]}, author={Jung, D. and Koo, H. J. and Whangbo, M. H.}, year={2000}, pages={113–119} } @article{jobic_brec_chateau_haines_leger_koo_whangbo_2000, title={Synthesis and crystal structure determination of a new pressure-induced iridium ditelluride phase, m-IrTe2, and comparison of the crystal structures and relative stabilities of various IrTe2 polymorphs}, volume={39}, ISSN={["0020-1669"]}, DOI={10.1021/ic000351e}, abstractNote={The new monoclinic IrTe2 phase m-IrTe2 was synthesized under pressure, and its structure was determined by X-ray powder diffraction. The relative stabilities of the three known and three hypothetical IrTe2 polymorphs were discussed on the basis of tight binding electronic band structure calculations. m-IrTe2 exhibits structural features of both CdI2- and pyrite-type IrTe2 phases and is expected to be nearly as stable as that of the CdI2-type IrTe2. The hypothetical IrS2- and ramsdellite-type IrTe2 phases are predicted to be more stable than the CdI2-type IrTe2.}, number={19}, journal={INORGANIC CHEMISTRY}, author={Jobic, S and Brec, R and Chateau, C and Haines, J and Leger, JM and Koo, HJ and Whangbo, MH}, year={2000}, month={Sep}, pages={4370–4373} } @article{koo_whangbo_1999, title={Analysis of bonding and d-electron count in the transition-metal carbides and transition-metal-silicide carbides with discrete linear M-C-M units (M = Cr, Fe, Re) by electronic structure calculations}, volume={38}, ISSN={["0020-1669"]}, DOI={10.1021/ic981309a}, abstractNote={Electronic structures of the silicide carbides Tm(2)Fe(2)Si(2)C, Th(2)Re(2)Si(2)C, and ThFe(2)SiC and the carbide Ho(2)Cr(2)C(3) were calculated, using the extended Hückel tight binding method, to probe the d-electron counts of their transition metal atoms M (Cr, Fe, Re) the bonding of their linear M-C-M (M = Cr, Fe, Re) units. The nature of the short interlayer X.X (X = C, Si) bonds in Tm(2)Fe(2)Si(2)C, Th(2)Re(2)Si(2)C, and Ho(2)Cr(2)C(3) was also examined. Our study shows that the M-C bonds of the M-C-M units exist as double bonds. There is significant bonding in the interlayer Si.Si contacts of the silicide carbides R(2)M(2)Si(2)C (M = Fe, Re). The transition-metal atoms exist as d(10) ions in Tm(2)Fe(2)Si(2)C and Th(2)Re(2)Si(2)C. The d-electron count is slightly lower than d(10) in ThFe(2)SiC and close to d(5) in Ho(2)Cr(2)C(3).}, number={9}, journal={INORGANIC CHEMISTRY}, author={Koo, HJ and Whangbo, MH}, year={1999}, month={May}, pages={2204–2210} } @article{koo_whangbo_1999, title={Analysis of the spin-spin interactions in layered oxides alpha '-NaV2O5, CaV2O5 and MgV2O5 and the spin-Peierls distortion in alpha '-NaV2O5 by molecular orbital, Madelung energy and bond valence sum calculations}, volume={111}, ISSN={["1879-2766"]}, DOI={10.1016/S0038-1098(99)00179-9}, abstractNote={The spin–spin exchange parameters of α′-NaV2O5, CaV2O5 and MgV2O5 were examined by calculating the spin–spin interaction energies of their spin dimers, and the probable pairing distortion leading to the (2a×2b×4c) superstructure of α′-NaV2O5 was investigated by performing Madelung energy and bond valence sum analyses. In the V2O5 layers of α′-NaV2O5, CaV2O5 and MgV2O5, ladder chains of vanadium atoms are arranged in a staggered manner. CaV2O5 and MgV2O5 have an unpaired spin at each vanadium site, while α′-NaV2O5 has one unpaired spin in each rung of the ladder chains. The latter makes α′-NaV2O5 behave as a spin 1/2 Heisenberg linear chain system. Madelung energy and bond valence sum calculations for α′-NaV2O5 show that the pairing distortion from the uniform spin lattice to the zigzag spin lattice proposed by Seo and Fukuyama is energetically favorable. In the zigzag spin lattice the paired spins do not reside in the ladder chains but in between the ladder chains, which makes α′-NaV2O5 different from a simple spin-Peierls system.}, number={7}, journal={SOLID STATE COMMUNICATIONS}, author={Koo, HJ and Whangbo, MH}, year={1999}, pages={353–360} } @article{lee_koo_ren_whangbo_1999, title={Calculations and analysis of the electronic structures of transition-metal phosphosilicides Cu4SiP8, IrSi3P3, CoSi3P3, and FeSi4P4}, volume={147}, ISSN={["0022-4596"]}, DOI={10.1006/jssc.1999.8142}, abstractNote={Abstract Electronic structures of phosphosilicides Cu4SiP8, IrSi3P3, CoSi3P3, and FeSi4P4 were calculated using the extended Huckel tight-binding method and were analyzed in terms of a modified electron counting scheme. The d-block levels of these compounds appear well below the Fermi level, thereby indicating that the transition-metal atoms exist as d10 ions. Except for the case of IrSi3P3, the d-block energy levels of these compounds occur in a narrow energy window less than 1.5 eV wide. The Si 3p orbitals act as acceptor orbitals to the transition-metal d orbitals in IrSi3P3, CoSi3P3, and FeSi4P4.}, number={1}, journal={JOURNAL OF SOLID STATE CHEMISTRY}, author={Lee, KS and Koo, HJ and Ren, J and Whangbo, MH}, year={1999}, month={Oct}, pages={11–18} } @article{suh_koo_watson_1999, title={Development of optimal HVI strength index for prediction of yarn tensile strength}, volume={1}, number={1999}, journal={Beltwide Cotton Conferences. Proceedings}, author={Suh, M. W. and Koo, H.-J. and Watson, M. D.}, year={1999}, pages={706–708} } @article{zhu_long_musfeldt_wei_sarrao_fisk_negishi_inoue_koo_whangbo_1999, title={High field optical response of eta-Mo4O11}, volume={9}, ISSN={["1155-4339"]}, DOI={10.1051/jp4:19991063}, number={P10}, journal={JOURNAL DE PHYSIQUE IV}, author={Zhu, Z and Long, VC and Musfeldt, JL and Wei, X and Sarrao, J and Fisk, Z and Negishi, H and Inoue, M and Koo, HJ and Whangbo, MH}, year={1999}, month={Dec}, pages={251–253} } @article{wang_vanzile_schlueter_geiser_kini_sche_koo_whangbo_nixon_winter_et al._1999, title={In-plane ESR microwave conductivity measurements and electronic band structure studies of the organic superconductor beta ''-(BEDT-TTF)(2)SF5CH2CF2SO3}, volume={103}, ISSN={["1089-5647"]}, DOI={10.1021/jp991268j}, abstractNote={The electronic structure of the organic superconductor {beta}''-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3} (BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) was characterized with the use of electron spin resonance (ESR) spectroscopy and electronic band structure calculations. The room-temperature ESR line width is 24-27 G in the plane of a donor molecule layer (i.e., in the ab-plane) and {approx}32 G along the normal to this plane (i.e., along the c*-direction). The ab-plane anisotropy of the microwave conductivity was extracted for the first time from the ESR Dysonian line shape analysis. The in-plane conductivity varies sinusoidally, is maximal along the interstack direction (b-axis), and is minimal along the donor stack direction (a-axis). The Fermi surfaces of the title compound consist of a 2D hole pocket and a pair of 1D wavy lines. The directions for the in-plane conductivity maximum and minimum are in excellent agreement with the electronic band structure calculated for {beta}''-(BEDT-TTF){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}, and the origin of the in-plane conductivity anisotropy lies in the one-dimensional part of the Fermi surface. This is the first time that an organic conductor shows Dysonian ESR line shape due to its 2D and strongly metallic nature, yet the 1D character is revealed simultaneously through themore » in-plane conductivity anisotropy.« less}, number={26}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={Wang, HH and VanZile, ML and Schlueter, JA and Geiser, U and Kini, AM and Sche, PP and Koo, HJ and Whangbo, MH and Nixon, PG and Winter, RW and et al.}, year={1999}, month={Jul}, pages={5493–5499} } @article{koo_suh_1999, title={Maximizing yarn and fabric strength through variance of HVI elongation}, volume={69}, ISSN={["0040-5175"]}, DOI={10.1177/004051759906900609}, abstractNote={ As a new method for maximizing yarn and fabric strengths, an exploratory blending experiment is completed in a 4-week period by processing 2117 bales of three different cottons in a textile mill to produce 94.4 tex (6.3/1 Ne) open-end spun yarns, and weaving them into a denim fabric. Bale selection is done in such a way that the variance of single fiber breaking elongations can be minimized within a laydown of 29 bales as well as among the fibers to be found within an arbitrary cross section of the yam produced from the laydown. The study shows that the variance of the HVI breaking elongations obtained from the cotton bales is useful for maximizing the resulting yarn strengths, especially when they are combined with the Mantis® single fiber test results. In addition, a follow-up study analyzes the HVI data and matching physical test data obtained from a 2-year production period. In all, 121,200 bales (4180 laydowns) are tested for HVI bundle strength, elongation, micronaire, length, and other properties. As in the exploratory study, the cotton bales are processed into 94.4 tex open-end spun yams and an identical denim fabric. The final analysis shows that the between-bale variance of HVI bundle breaking elongations within a laydown is quite useful as a criterion for bale selection and yarn and fabric strength maximization. An enhanced method is also developed to make use of the HVI elongation data together with the Mantis single fiber tensile test results. The new procedure is even more effective at maximizing yarn and fabric strengths. }, number={6}, journal={TEXTILE RESEARCH JOURNAL}, author={Koo, HJ and Suh, MW}, year={1999}, month={Jun}, pages={447–456} } @article{long_zhu_musfeldt_wei_koo_whangbo_jegoudez_revcolevschi_1999, title={Polarized optical reflectance and electronic band structure of alpha '-NaV2O5}, volume={60}, ISSN={["2469-9969"]}, DOI={10.1103/physrevb.60.15721}, abstractNote={We report polarized optical reflectance studies of {alpha}{sup '}-NaV{sub 2}O{sub 5} between 0.5 and 6 eV as a function of temperature (T) and magnetic field (H). The electronic excitations and their polarization dependence are interpreted according to our extended Hueckel tight-binding polarized band structure calculations. Strong bands near 1 eV in both chain and rung directions are attributed to V d{yields}d transitions. Charge transfer excitations are estimated to begin near 3.3 eV and have significant strength at 4.4 eV and above. The reflectance ratios, {delta}R(T)=R(T)/R(T=4 K), measured at H=0 and 28 T, reveal broad polarization-dependent changes through the low temperature transition, T{sub c}. Integrated intensities of {delta}R features exhibit a second-order transition at 36 K in zero field and at 33{+-}1 K in high field, consistent with a spin-Peierls aspect to the phase transition. (c) 1999 The American Physical Society.}, number={23}, journal={PHYSICAL REVIEW B}, author={Long, VC and Zhu, Z and Musfeldt, JL and Wei, X and Koo, HJ and Whangbo, MH and Jegoudez, J and Revcolevschi, A}, year={1999}, month={Dec}, pages={15721–15727} } @article{lee_koo_whangbo_1999, title={Spin-spin interactions in the oxides A(3)M ' MO6 (M = Rh, Ir; A = Ca, Sr; M ' = alkaline earth, Zn, Cd, Na) of the K4CdCl6 structure type examined by electronic structure calculations}, volume={38}, ISSN={["0020-1669"]}, DOI={10.1021/ic9813819}, abstractNote={The oxides A(3)M'MO(6) (M = Rh, Ir; A = Ca, Sr; M' = alkaline earth, Zn, Cd) of the K(4)CdCl(6) structure type consist of isolated (MO(6))(8)(-) octahedral anions and exhibit an antiferromagnetic ordering at low temperatures. The spin-spin interactions in these oxides, Ca(3)NaMO(6) (M = Ir, Ru), and Sr(3)NaRuO(6) were examined by calculating how strongly the t(2g)-block levels of adjacent (MO(6))((6+)(n)()())(-) (n = 1, 2) anions interact in the presence and absence of the intervening cations A(2+) and M' (n)()(+) (n = 1, 2). Our calculations show that the spin-spin interactions in these oxides are three-dimensional, and the superexchange interactions occur mainly through the short intrachain and interchain M-O.O-M linkages. When the M(n)()(+) cation is very small compared with the A(2+) cation, the intrachain interaction is substantially stronger than the interchain interaction. The opposite is found when the sizes of the M(n)()(+) and A(2+) cations become similar.}, number={9}, journal={INORGANIC CHEMISTRY}, author={Lee, KS and Koo, HJ and Whangbo, MH}, year={1999}, month={May}, pages={2199–2203} } @article{suh_koo_watson_1998, title={Estimation of HVI bundle modulus and toughness as determinants to tensile properties of spun yarns}, volume={2}, number={1998}, journal={Beltwide Cotton Conferences. Proceedings}, author={Suh, M. W. and Koo, H.-J. and Watson, M. D.}, year={1998}, pages={1530–1536} } @article{koo_whangbo_mccarroll_greenblatt_gautier_halet_gougeon_1998, title={On the origin of the anomalous electrical resistivity of LnMo(5)O(8) (Ln = trivalent rare earth)}, volume={108}, ISSN={["0038-1098"]}, DOI={10.1016/S0038-1098(98)00407-4}, abstractNote={Electronic structures of AMo5O8 (A=rare earth, alkaline earth) and the solid solution Sr1−xLaxMo5O8 (x=0–1) were examined using the extended Hückel tight binding method. AMo5O8 phases with divalent A cations (A=Sr, Ca, Eu) are normal semiconductors with small band gap. The Fermi surfaces of Sr1−xLaxMo5O8 (0.0