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Konstantinović, M.J.; Konstantinović, Z.; Popović, Zdenka

doi:10.1103/physrevb.54.68

Cited by 16 publications

(18 citation statements)

References 12 publications

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“…11 gives very similar values for J's. Thus, our results confirm the formation of singlet Ti-Ti dimers in the LT phase of NaTiSi 2 O 6 , as originally proposed [1,2]. The spin-gap would be even bigger then the one found in the experiment, ∆ exp ∼500 K [1].…”

supporting

confidence: 90%

“…Our calculations demonstrate the formation of singlet Ti-Ti dimers in LT phase of NaTiSi 2 O 6 driven by corresponding orbital ordering [2] …”

mentioning

confidence: 72%

“…A rather rare phenomenon of an opening of the spin gap in transition metal oxides was observed in pyroxene NaTiSi 2 O 6 and was interpreted as a formation of singlet Ti-Ti dimers [1,2]. However, in the recent Letter [3] the authors challenged this picture.…”

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confidence: 99%

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Comment on “Sodium PyroxeneNaTiSi2O6: Possible Haldane Spin-1 Chain System”

2006

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A rather rare phenomenon of an opening of the spin gap in transition metal oxides was observed in pyroxene NaTiSi 2 O 6 and was interpreted as a formation of singlet Ti-Ti dimers [1,2]. However, in the recent Letter [3] the authors challenged this picture. On the basis of spin polarized GGA calculations they argued that with decrease of the temperature this compound evolves into a Haldane phase, characterized by formation of onedimensional S=1 chains.This novel interpretation, however, is highly questionable. The authors claim that "direct overlap between 3d orbitals centered on closer Ti ions, ..., indicates that two electrons of the same spin, occupying those states, are shared by two Ti ions" (cursive ours). This picture however contradicts typical situation for shorts metalmetal bonds in insulating solids, especially those of spin S = 1/2 ions.Most probably the defect lies in the neglect of electronic correlations in the calculation method used in [3]. NaTiSi 2 O 6 is known to be strong Mott insulator with the energy gap close to 2 eV [4], whereas the calculations of Ref. 3 lead to very small energy gaps 0.2-0.3 eV.In order to take into account strong electronic correlations in Ti-3d shell, we performed for the LT phase (T=100 K) of NaTiSi 2 O 6 the LDA+U calculations [5], which was proven very successful in similar cases [6,7,8] The calculation scheme was realized in the framework of the linear muffin-tin orbitals method [9]. Crystal structure parameters were taken from Ref. 10. The values of on-cite Coulomb interaction U = 3.3 eV and Hund's rule exchange J H = 0.8 eV parameters for Ti-3d shell were obtained in constrained supercell calculation [7].In contrast to Ref. 3, the fully antiferromagnetic state (AFM) was found to have lowest total energy (see Tab.1). The total energy of F+AF state (ferromagnetically coupled antiferromagnetic dimers on short Ti-Ti bonds) is just a little bit larger. This indicates that the coupling between dimers is pretty small, J inter = 7 K. On the contrary, the exchange interaction within Ti dimers is antiferromagnetic and rather strong: from the comparison of total energies of totally AFM and AF+F states we find J intra = 626 K. Direct calculation of exchange integrals using the scheme of Ref. In conclusion, we stress that by neglecting correlation effects [3]

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supporting

confidence: 90%

“…Our calculations demonstrate the formation of singlet Ti-Ti dimers in LT phase of NaTiSi 2 O 6 driven by corresponding orbital ordering [2] …”

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confidence: 72%

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Comment on “Sodium PyroxeneNaTiSi2O6: Possible Haldane Spin-1 Chain System”

2006

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“…However, the orientation of Cu spins was not unambiguously determined and two magnetic structures were proposed -one with spins parallel to the c axis 7,10 and one with spins within the ab plane 11 . Optical spectroscopy experiments including polarized far-infrared and Raman spectra on single crystals suggest the c axis orientation of copper spins [12][13][14][15] . Specific heat and thermal expansion studies of the critical behavior around T N are consistent with the 3D Ising universality class, thus, also suggesting an easy c axis anisotropy 16 .…”

Section: Introductionmentioning

confidence: 99%

Magnetically induced ferroelectricity in Bi2CuO4

et al. 2017

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The tetragonal copper oxide Bi2CuO4 has an unusual crystal structure with a three-dimensional network of well separated CuO4 plaquettes. This material was recently predicted to host electronic excitations with an unconventional spectrum and the spin structure of its magnetically ordered state appearing at TN∼ 43 K remains controversial. Here we present the results of detailed studies of specific heat, magnetic and dielectric properties of Bi2CuO4 single crystals grown by the floating zone technique, combined with the polarized neutron scattering and high-resolution X-ray measurements. Our polarized neutron scattering data show Cu spins are parallel to the ab plane. Below the onset of the long range antiferromagnetic ordering we observe an electric polarization induced by an applied magnetic field, which indicates inversion symmetry breaking by the ordered state of Cu spins. For the magnetic field applied perpendicular to the tetragonal axis, the spin-induced ferroelectricity is explained in terms of the linear magnetoelectric effect that occurs in a metastable magnetic state. A relatively small electric polarization induced by the field parallel to the tetragonal axis may indicate a more complex magnetic ordering in Bi2CuO4.

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“…Synthesis of isatin-3-(4`-hydroxy)benzoylhydrazone Isatin-3-(4`-hydroxy)benzoylhydrazone was prepared by the reaction of the equimolar amount of isatin (1.47g) and 4-hydroxybenzoylhydrazide (1.52g) in 95 % ethanol following the standard procedure [6,7]. The mixture was refluxed at 50 0 C for 60 min.…”

Section: Methodsmentioning

confidence: 99%