Search

A series of DFT calculations for two layered compounds with honeycomb lattice-α-TiCl 3 and α-TiBr 3 has been performed. It was shown that the symmetric SU(4) spin-orbital model recently proposed for d 1 systems with honeycomb lattice cannot be realized in these titanates because they dimerize in the low temperature phase. This explains experimentally observed drop in magnetic susceptibility of α-TiBr 3 . Our results also suggest formation of valence-bond liquid state in the high-temperature phase of α-TiCl 3 and α-TiBr 3 ., (© 2021 IOP Publishing Ltd.)

Uniform quasi-one-dimensional integer spin compounds are of interest as a potential realization of the Haldane conjecture of a gapped spin liquid. This phase, however, has to compete with magnetic anisotropy and long-range ordered phases, the implementation of which depends on the ratio of interchain J' and intrachain J exchange interactions and both uniaxial D and rhombic E single-ion anisotropies. Strontium nickel selenite chloride, Sr 2 Ni(SeO 3 ) 2 Cl 2 , is a spin-1 chain system which passes through a correlations regime at T max  ~ 12 K to long-range order at T N  = 6 K. Under external magnetic field it experiences the sequence of spin-flop at B c1  = 9.0 T and spin-flip transitions B c2  = 23.7 T prior to full saturation at B sat  = 31.0 T. Density functional theory provides values of the main exchange interactions and uniaxial anisotropy which corroborate the experimental findings. The values of J'/J = 0.083 and D/J = 0.357 place this compound into a hitherto unoccupied sector of the Sakai-Takahashi phase diagram., (© 2021. The Author(s).)

We present measurements of resistivity, x-ray absorption (XAS) and emission (XES) spectroscopy together with ab initio band structure calculations for quasi two dimensional ruthenate Na 2 RuO 3 . Density function calculations (DFT) and XAS and XES spectra both show that Na 2 RuO 3 is a semiconductor with an activation energy of  ∼80 meV. Our DFT calculations reveal large magneto-elastic coupling in Na 2 RuO 3 and predict that the ground state of Na 2 RuO 3 should be antiferromagnetic zig-zag.

CuAl 2 O 4 is a normal spinel oxide having quantum spin, S  =  1/2 for Cu 2+ . It is a rather unique feature that the Cu 2+ ions of CuAl 2 O 4 sit at a tetrahedral position, not like the usual octahedral position for many oxides. At low temperatures, it exhibits all the thermodynamic evidence of a quantum spin glass. For example, the polycrystalline CuAl 2 O 4 shows a cusp centered at ~2 K in the low-field dc magnetization data and a clear frequency dependence in the ac magnetic susceptibility while it displays logarithmic relaxation behavior in a time dependence of the magnetization. At the same time, there is a peak at ~2.3 K in the heat capacity, which shifts towards a higher temperature with magnetic fields. On the other hand, there is no evidence of new superlattice peaks in the high-resolution neutron powder diffraction data when cooled from 40 to 0.4 K. This implies that there is no long-ranged magnetic order down to 0.4 K, thus confirming a spin glass-like ground state for CuAl 2 O 4 . Interestingly, there is no sign of structural distortion either although Cu 2+ is a Jahn-Teller active ion. Thus, we claim that an orbital liquid state is the most likely ground state in CuAl 2 O 4 . Of further interest, it also exhibits a large frustration parameter, f  =  |θ CW /T m | ~ 67, one of the largest values reported for spinel oxides. Our observations suggest that CuAl 2 O 4 should be a rare example of a frustrated quantum spin glass with a good candidate for an orbital liquid state.

An unusual effect was discovered in Li et al (2010 J. Solid State Chem. 183 1388): the substitution of nonmagnetic low-spin Co(3+) in LaCoO3 by the formally isoelectronic and also nonmagnetic Rh(3+) led, surprisingly, to a rapid appearance of magnetism in LaCo(1-x)Rh(x)O3, even for small amounts of doping. Different explanations for this effect were proposed in the literature. To clarify the situation we carried out unbiased ab initio calculations of this system. We concluded that, in agreement with the original assumption of Li et al, but in contrast with later statements (Knizek et al 2012 Phys. Rev. B 85 134401), this effect is caused by the valence change ('redox reaction') Co(3+) +  Rh(3+) → Co(2+) +  Rh(4+), which creates magnetic Co(2+) and Rh(4+) ions. For the half-filled case LaCo1/2Rh1/2O3 we obtained the state with charge ordering of Co(2+) and Rh(4+) ions, which according to our calculations are antiferromagnetically coupled. The obtained results reasonably explain the observed behavior of the magnetic susceptibility of LaCo(1-x)Rh(x)O3, and the novel state predicted at half-doping could be verified experimentally by detailed structural and magnetic studies and by x-ray absorption spectroscopy.