High-pressure effect on the crystal and magnetic structure of LuMnO3: Correlation between a distortion of the triangular lattice and the symmetry of the magnetic state in hexagonal frustrated manganites

The effect of a high pressure (up to 6 GPa) on the crystal and magnetic structure of the hexagonal manganite LuMnO₃ is studied by neutron diffraction in the temperature range 10–295 K. It is found that, as the pressure increases, the ordered magnetic moment of Mn ions at T = 10 K decreases noticeably from 2.48 (0 GPa) to 1.98 μ_B (6 GPa). This decrease is due to an enhancement of the geometrical frustration effects on the triangular lattice. At the same time, the symmetry of the triangular antiferromagnetic state (the irreducible representation Γ₂) remains unchanged. A correlation is revealed between the distortion parameter of the triangular lattice formed by Mn ions and the symmetry of the antiferromagnetic state of hexagonal manganites RMnO₃. Based on this correlation, a generalized magnetic phase diagram of these compounds is constructed. The obtained phase diagram provides an explanation for the changes observed in the magnetic state of hexagonal manganites caused by high pressure and chemical substitution.     

Use of stabilized adsorbents for collecting extracts after supercritical fluid extraction

A method was proposed for preconcentrating small amounts of numerous organic contaminants. The method is based on supercritical fluid extraction and trapping the extracted compounds with a multilayer adsorption device followed by their thermodesorption directly to a gas chromatographic system. A method was described for preparing stabilized adsorbents on the basis of a support with a stationary phase using sol-gel synthesis.     

Calculation of the energies of interatomic and intermolecular van der Waals interactions in terms of variational perturbation theory

A new quantum mechanical method is suggested for calculating separate contributions to the energies of interatomic and intermolecular van der Waals interactions. The method involves the multipole expansion of the electrostatic potential of two interacting charge systems, which is treated as a perturbation. Equations for the induction and dispersion contributions are obtained by varying the second-order correction to the interaction energy. The wave functions of isolated systems in the ground state are taken in single determinatal form. The excited-state wave functions are expressed as superpositions of singly excited configurations (the Tamm-Dankov approximation). The density matrix formalism allowed us to obtain the equations in compact matrix form. The method is applied to calculations of the dispersion energies of interactions between two- and four-electron atoms and between two benzene molecules. M. E. Evsev'ev State Pedagogical Institute, Mordoviya. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 4, pp. 600–607, July–August, 1995. Translated by I. Izvekova     

Synthesis of 1,1-dihydroperfluorooxaalkan-1-ols and their interaction with terephthaloyl chloride

A series of 1,1-dihydroperfluorooxaalkan-1-ols and ,,,-tetrahydroperfluorooxaalkanediols has been synthesized. Some tercphthalates were synthesized by the reaction of these alcohols and diols with terephthaloyl chloride.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1573–1576, June, 1996.     

Time-of-flight neutron spectrometer for micro sample studies under high pressure

Abstract

A new neutron spectrometer for investigations of elastic and inelastic neutron scattering on polycrystal microsamples under high pressure in diamond and sapphire anvils cells is described. The spectrometer is operating at the IBR-2 pulsed reactor at JINR. The time-of-flight method and ring-shaped multicounter detector are used to register the scattered neutrons. Parameters and methodical peculiarities of the device and the examples of experimental studies are given.     

Study of Medieval Russian Enamel Pendant Using a Complex of Nondestructive Methods

Crystallography Reports - A medieval Russian bronze pendant icon with enamel images, dated to the period from the 12th to the first half of the 13th century was studied. The investigation was...     

Transformation of the magnetic structure of FeBO<Subscript>3</Subscript> under high pressures

The transformation of magnetic structure under hydrostatic and quasi-hydrostatic pressures up to 4 GPa was studied for iron borate FeBO₃ by the neutron diffraction method. Under quasi-hydrostatic conditions, the orientation of iron magnetic moments changes at pressures P≥1.4 GPa. Under hydrostatic conditions, no changes in the magnetic structure of iron borate were observed up to 2.1 GPa. This behavior is caused by the influence of the inhomogeneity (in magnitude and direction) of elastic stresses on the configuration of magnetic sublattices.     

Preparation and properties of some derivatives of perfluoropropyl vinyl ether

Conclusions It has been shown that it is possible to synthesize phenoxy derivatives of perfluoroalkyl ethers from perfluoropropyl vinyl ether. Some reactions of the products have been studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2319–2321, October, 1984.     

Magnetic density of states at low energy in geometrically frustrated systems

Using muon-spin-relaxation measurements we show that the pyrochlore compound Gd(2)Ti(2)O(7), in its magnetically ordered phase below approximately 1 K, displays persistent spin dynamics down to temperatures as low as 20 mK. The characteristics of the induced muon relaxation can be accounted for by a scattering process involving two magnetic excitations, with a density of states characterized by an upturn at low energy and a small gap depending linearly on the temperature. We propose that such a density of states is a generic feature of geometrically frustrated magnetic materials.