Search

The silver ruthenium oxide AgRuO3 consists of honeycomb Ru25+O62- layers and can be considered an analogue of SrRu2O6 with a different intercalation. We present measurements of magnetic susceptibility and specific heat on AgRuO3 single crystals, which reveal a sharp antiferromagnetic transition at 342(3) K. The electrical transport in single crystals of AgRuO3 is determined by a combination of activated conduction over an intrinsic semiconducting gap of ≈100 meV and carriers trapped and thermally released from defects. From powder neutron diffraction data a Néel-type antiferromagnetic structure with the Ru moments along the c axis is derived. Raman spectroscopy on AgRuO3 single crystals and muon spin rotation spectroscopy on powder samples indicate a further weak phase transition or a crossover in the temperature range 125-200 K. The transition does not show up in the magnetic susceptibility, and its origin is argued to be related to defects but cannot be fully clarified. The experimental findings are complemented by density-functional-theory-based electronic structure calculations. It is found that the magnetism in AgRuO3 is similar to that in SrRu2O6, however, with stronger intralayer and weaker interlayer magnetic exchange interactions. © 2021 authors. Published by the American Physical Society.

First-principles calculations and a model consideration of magnetically frustrated layered material PdCrO2 are performed. The results on the exchange parameters are in agreement with the experimental data on the Curie-Weiss temperature (θ). We show that experimentally observed strong suppression of the Néel temperature (TN) in comparison with the Curie-Weiss temperature is due to three main factors. First, as expected, this is connected with the layered structure and relatively small exchange interaction along the c axis. Second, deformation of the ideal in-plane 120° magnetic structure is crucial to provide finite TN value. However, these two factors are still insufficient to explain low TN and the large frustration factor |θ|/TN. Thus, we suggest a scenario of an exotic non-Fermi-liquid state in PdCrO2 above TN within the frameworks of the Anderson lattice model, which seems to explain qualitatively all its main peculiarities. © 2020 American Physical Society.

MnSnTeO6, a new chiral antiferromagnet, was prepared both by topotactic transformation of the metastable rosiaite-type polymorph and by direct synthesis from coprecipitated hydroxides. Its structure and its static and dynamic magnetic properties were studied comprehensively both experimentally (through X-ray and neutron powder diffraction, magnetization, specific heat, dielectric permittivity, and ESR techniques) and theoretically (by means of ab initio density functional theory (DFT) calculations within the spin-polarized generalized gradient approximation). MnSnTeO6 is isostructural with MnSb2O6 (space group P321) and does not show any structural transition between 3 and 300 K. The magnetic susceptibility and specific heat exhibit an antiferromagnetic ordering at TN ≈ 9.8 K, which is confirmed by low-temperature neutron data. At the same time, the thermodynamic parameters demonstrate an additional anomaly on the temperature dependences of magnetic susceptibility χ(T), specific heat Cp(T) and dielectric permittivity ϵ(T) at T∗ ≈ 4.9 K, which is characterized by significant temperature hysteresis. Clear enhancement of the dielectric permittivity at T∗ is most likely to reflect the coupling of dielectric and magnetic subsystems leading to development of electric polarization. It was established that the ground state of MnSnTeO6 is stabilized by seven exchange parameters, and neutron diffraction revealed incommensurate magnetic structure with propagation vector k = (0, 0, 0.183) analogous to that of MnSb2O6. Ab initio DFT calculations demonstrate that the strongest exchange coupling occurs between planes along diagonals. All exchange parameters are antiferromagnetic and reveal moderate frustration. Copyright © 2020 American Chemical Society.

Investigation of the recently synthesized series of isostructural compounds Ba4NbTM3O12 (TM=Mn, Rh, and Ir) with transition-metal trimers in a face-sharing geometry makes it possible to examine a tendency to the molecular orbitals (MO) formation going from 3d to 5d transition metal ions. Our ab initio calculations of electronic and magnetic properties describe the experimental findings and demonstrate gradual transition from the picture of localized electrons for Mn to the MO picture for Rh and especially for Ir. We also show that the often used criterion, according to which the metal-metal distance in a compound shorter than in a respective metal always gives MO, may break down in some cases. © 2020 American Physical Society.

The tetradymite compound BiSbTeSe2 is one of the most bulk-insulating three-dimensional topological insulators, which makes it important in topological insulator research. It is a member of the solid-solution system Bi2-xSbxTe3-ySey, for which the local crystal structure, such as the occupation probabilities of each atomic site, is not well understood. We have investigated the temperature- and polarization-dependent spontaneous Raman scattering in BiSbTeSe2, revealing a much higher number of lattice vibrational modes than predicted by group-theoretical considerations for the space group R3m corresponding to an ideally random solid-solution situation. The density-functional calculations of phonon frequencies show a very good agreement with experimental data for parent material Bi2Te3, where no disorder effects were found. In comparison to Bi2Te3 the stacking disorder in BiSbTeSe2 causes a discrepancy between theory and experiment. Combined analysis of experimental Raman spectra and density-functional-theory-calculated phonon spectra for different types of atomic orders showed coexistence of different sequences of layers in the material and that those with Se in the center and a local order of Se-Bi-Se-Sb-Te are the most favored. © 2019 American Physical Society.

We report results of the Raman measurements for SrRu2O6 having extraordinary high Néel temperature for a layered material. No additional phonon modes were detected at the temperature of magnetic transition thus excluding lowering of the symmetry in the magnetically ordered phase. An unusual increase in softening and damping of some phonons as the temperature approaches TN indicates the appearance of a continuum of interacting electronic excitations at T≥300K. We also observe an intensive Raman response at 2050 cm-1. Analysis of the polarization dependence and comparison with available theoretical data shows that this peak likely originates from the transitions between molecular orbitals previously proposed to explain the magnetic properties of SrRu2O6. It can be explained by two magnon excitations only if the magnon bandwidth is ∼140 meV. © 2019 American Physical Society.

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. © 2019, Pleiades Publishing, Inc.

The magnon dispersion of Ca2RuO4 has been studied by polarized and unpolarized neutron scattering experiments on crystals containing 0, 1, and 10% of Ti. Ti is inserted in order to enable the growth of large, partially detwinned crystals. One percent of Ti has a negligible impact on structural and magnetic properties. Also for 10% Ti content magnetic properties still change very little, but the insulating phase is stabilized up to at least 700 K and structural distortions are reduced. The full dispersion of transverse magnons studied for 1% Ti substitution can be well described by a conventional spin-wave model with interaction and anisotropy parameters that agree with density functional theory calculations. Spin-orbit coupling strongly influences the magnetic excitations, as it is most visible in large energies of the magnetic zone-center modes arising from magnetic anisotropy. Additional modes appear at low energy near the antiferromagnetic zone center and can be explained by a sizable magnetic moment of 0.11 Bohr magnetons, which the density functional theory calculations find located on the apical oxygens. The energy and the signal strength of the additional branch are well described by taking into account this oxygen moment with weak ferromagnetic coupling to the Ru moments.

В социокультурном пространстве выполнен поиск методологического аналога для рефлексии феномена ядерной энергии с позиций представлений о человеке и обществе. Полезным признано обращение к антропосоциальной компоненте Православия. Оконтурено представление о вселенском и цивилизационном родстве феноменов. Сформулированы основные вопросы применительно к их сопряжению, намечены варианты ответов. Приведены конкретные примеры, при анализе которых предлагаемый методологический перенос мог бы быть реализован., Within the socio-cultural space the search of methodology analogous for the phenomenon of nuclear energy reflection from the perspective of man and society presentation is made. Reference to the anthropo-social component of Orthodoxy has been proven to be useful. There has been outlined the idea about the universal and civilization relationship of these phenomena. The main questions concerning their connection have been formulated as well as some ways to answer them are done. Some examples which have been used for analyzing the possibility of the suggested methodological transfer realization are given.

This paper presents further consideration of the following interrelation in the energy production sphere: oil and gas business and international projects on the long-term storage of nuclear materials. There are discussed some Russian versions of construction of nuclear depositories as well as corresponding geological assessments. In particular, for the North-West Russia.

Рассматриваются характерные особенности апеллятивных текстов, объединенных функцией побуждения адресата к совершению определенного действия. Делается вывод, что апеллятивные тексты характеризуются ориентацией на конкретного адресата, эксплицитной антропоцентричностью, что выражается в их диалогическом характере и четкой адресованности, заложенной в основу текстопорождения., The article studies the peculiarities of appellative texts whose universal feature is the function of prompting their addressee to perform a certain action. The author concludes that appellative texts are addressee-oriented; possess a pronounced anthropocentricism, revealed through their dialogical character and addressedness, being a basis for text-generation.

Общефилологические основы понимания диалогичности, трактующиеся в современных исследованиях как фундаментальное свойство всякой речи, ее адресованность, рассматриваются на примере апеллятивных текстов, отличающихся четкой ориентацией на конкретного читателя, эксплицитной антропоцентричностью. Прагматическая направленность апеллятивных текстов, обусловливает наличие маркеров диалогичности, отражающих двуначалие коммуникации, репрезентирующих факт личностно ориентированного общения и организующих «дистантный диалог»., The article analyses the universal philological understanding of dialogicality defined as a fundamental characteristic of any kind of speech in contemporary research works and its addressedness with reference to appellative texts, characterized by a clear appeal to the reader, and explicit anthropocentrism. The pragmatic orientation of appellative texts conditions the existence of dialogicality markers, reflecting the two-sidedness of communication, representing personality oriented communication and organizing a 'distant dialogue'.