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The results of full study of X-ray photoelectron spectra (XPS) of spin-liquid candidate CuAl2O4 including the measurements of high-energy resolved core level (Cu , Al , O ), Cu LMM Auger and valence band spectra are presented. The comparison of obtained results with spectra of reference samples and specially performed density functional theory calculations has confirmed a finite Cu site-disorder in CuAl2O4, where about 30% of Cu2+ ions occupy the octahedral sites. Obtained valence band spectra can be used in further theoretical studies aimed on the investigation of electronic and magnetic properties of this mysterious ma-terial. [ABSTRACT FROM AUTHOR]

We study physical properties of layered α-ZrCl3 as a potential candidate for the physical realization of the SU(4) spin—orbital model. Both DFT and DFT + U + SOC calculations show that this material most probably dimerizes at normal conditions. Therefore, it is unlikely that the symmetric SU(4) model can be used for description of magnetic properties of α-ZrCl3 at low temperatures. In the dimerized structure electrons occupy molecular orbitals formed by the xy orbitals. One might expect a nonmagnetic ground state in this case. Interestingly the energy difference between various dimer packings is rather small and thus dimers may start to flow over the lattice as they do in Li2RuO3. [ABSTRACT FROM AUTHOR]

The electronic and magnetic properties of clinopyroxene CaMnGe2O6 were studied using density function calculations within the GGA + U approximation. It is shown that anomalous ferromagnetic ordering of neighboring chains is due to a "common-enemy" mechanism. Two antiferromagnetic exchange couplings between nearest neighbors within the Mn-Mn chain and interchain coupling via two GeO4 tetrahedra suppress antiferromagnetic exchange via single GeO4 tetrahedron and stabilize ferromagnetic ordering of Mn chains. [ABSTRACT FROM AUTHOR]

In the present paper, the electronic, magnetic, and structural properties of a novel system FeZnMo3O8 with a polar crystal structure are investigated using GGA + U (Generalized gradient approximation taking into account Coulomb correlations) calculations. It is shown that Fe ions preferably occupy octahedral and Zn ions tetrahedral positions. This structural feature is caused by different ionic radii of these ions and not by the exchange coupling. The calculated exchange constants naturally explain magnetic structure observed in this material. [ABSTRACT FROM AUTHOR]

In the present paper, the electronic, magnetic, and structural properties of a novel system FeZnMo3O8 with a polar crystal structure are investigated using GGA + U (Generalized gradient approximation taking into account Coulomb correlations) calculations. It is shown that Fe ions preferably occupy octahedral and Zn ions tetrahedral positions. This structural feature is caused by different ionic radii of these ions and not by the exchange coupling. The calculated exchange constants naturally explain magnetic structure observed in this material. [ABSTRACT FROM AUTHOR]

The structural properties of Na2RuO3 under pressure are studied using density functional theory within the nonmagnetic generalized gradient approximation (GGA). We found that one may expect a structural transition at ∼3 GPa. This structure at the high-pressure phase is exactly the same as the low-temperature structure of Li2RuO3 (at ambient pressure) and is characterized by the P21/m space group. Ru ions form dimers in this phase and one may expect strong modification of the electronic and magnetic properties in Na2RuO3 at pressure higher than 3 GPa. [ABSTRACT FROM AUTHOR]

We report the revised crystal structure, static and dynamic magnetic properties of quasi-two dimensional honeycomb-lattice silver delafossite Ag3Co2SbO6. The magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long range order at low temperatures with Néel temperature TN∼ 21.2 K. In addition, the magnetization curves revealed a field-induced (spin–flop type) transition below TN in moderate magnetic fields. The GGA+U calculations show the importance of the orbital degrees of freedom, which maintain a hierarchy of exchange interaction in the system. The strongest antiferromagnetic exchange coupling was found in the shortest Co–Co pairs and is due to direct and superexchange interaction between the half-filled xz + yz orbitals pointing directly to each other. The other four out of six nearest neighbor exchanges within the cobalt hexagon are suppressed, since for these bonds the active half-filled orbitals turned out to be parallel and do not overlap. The electron spin resonance (ESR) spectra reveal a broad absorption line attributed to the Co2+ ion in an octahedral coordination with an average effective g-factor g = 2.40 ± 0.05 at room temperature and show strong divergence of the ESR parameters below ∼150 K, which implies an extended region of short-range correlations. Based on the results of magnetic and thermodynamic studies in applied fields, we propose a magnetic phase diagram for the new honeycomb-lattice delafossite. [ABSTRACT FROM AUTHOR]

We present the ab initio calculation of the electronic structure and magnetic properties of Bi2Fe4O9. This compound crystallizes in the orthorhombic crystal structure with the Fe3+ ions forming the Cairo pentagonal lattice implying strong geometric frustration. The neutron diffraction measurements reveal nearly orthogonal magnetic configuration, which at first sight is rather unexpected since it does not minimize the total energy of the pair of magnetic ions coupled by the Heisenberg exchange interaction. Here, we calculate the electronic structure and exchange integrals of Bi2Fe4O9 within the LSDA+U method. We obtain three different in-plane (J3=36 K, J4=73 K, J5=23 K) and two interplane (J1=10 K, J2=12 K) exchange parameters. The derived set of exchange integrals shows that the realistic description of Bi2Fe4O9 needs a more complicated model than the ideal Cairo pentagonal lattice with only two exchange parameters in the plane. However, if one takes into account only the two largest exchange integrals, then according to the ratio x=J3/J4=0.49

An unusual orbital state was recently proposed to explain the magnetic and transport properties of Ba3CoRu2O9 [H. Zhou et al., Phys. Rev. B. 85, 041201 (2012)]. We show that this state contradicts the first Hund's rule and does not realize in the system under consideration because of a too small crystal-field splitting in the r2~ shell. A strong suppression of the local magnetic moment in Ba3CoRu2O9 is attributed to a strong hybridization between the Ru 4d and O 2p states. [ABSTRACT FROM AUTHOR]

We report the revised crystal structure, static and dynamic magnetic properties of quasi-two dimensional honeycomb-lattice silver delafossite Ag3Co2SbO6. The magnetic susceptibility and specific heat data are consistent with the onset of antiferromagnetic long range order at low temperatures with Néel temperature TN∼ 21.2 K. In addition, the magnetization curves revealed a field-induced (spin–flop type) transition below TN in moderate magnetic fields. The GGA+U calculations show the importance of the orbital degrees of freedom, which maintain a hierarchy of exchange interaction in the system. The strongest antiferromagnetic exchange coupling was found in the shortest Co–Co pairs and is due to direct and superexchange interaction between the half-filled xz + yz orbitals pointing directly to each other. The other four out of six nearest neighbor exchanges within the cobalt hexagon are suppressed, since for these bonds the active half-filled orbitals turned out to be parallel and do not overlap. The electron spin resonance (ESR) spectra reveal a broad absorption line attributed to the Co2+ ion in an octahedral coordination with an average effective g-factor g = 2.40 ± 0.05 at room temperature and show strong divergence of the ESR parameters below ∼150 K, which implies an extended region of short-range correlations. Based on the results of magnetic and thermodynamic studies in applied fields, we propose a magnetic phase diagram for the new honeycomb-lattice delafossite. [ABSTRACT FROM AUTHOR]