Study of the magnetic properties of the permanent magnets by Mössbauer spectroscopy

This paper presents methods that can be used in order to determine the relative remanent magnetization and uniaxial magnetic anisotropy constant of particles in powder-based permanent magnets using Mössbauer spectroscopy. The methods were verified on the permanent magnet barium ferrite.     

Study of the Chelyabinsk Meteorite Magnetism by Nuclear Gamma-Resonance Spectroscopy

Crystallography Reports - Three fragments of the Chelyabinsk meteorite have been investigated by Mössbauer spectroscopy in a temperature range of 300–830 K. They are found to contain...     

Chitosans: Thermochemical Study

The physical and phase transitions of a series of chitosans differing in molecular weight and deacetylation degree have been revealed by means of differential scanning calorimetry, thermogravimetry, and mass spectrometry. The temperature ranges corresponding to the dehydration and thermolysis of the considered polymers have been determined. The devitrification temperature of the polymers has been recorded, and its two-parametric regression on the chitosans molecular weight and deacetylation degree has been found. The molecular weight of the polymer revealed stronger effect on the devitrification temperature in comparison with the deacetylation degree.     

X-Ray Diffraction and Mössbauer Studies of the Structural Features of BiFe<Subscript>1 ‒ <Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>3</Subscript> Multiferroics

The structure of ceramic BiFe_1?xZn_xO₃ multiferroic samples is investigated using the X-ray diffraction method and Mössbauer spectroscopy. X-ray diffraction analysis of the samples indicates the existence of the Bi₁₂(Bi_0.5Fe_0.5)O_19.5 impurity phase. High-temperature heating of the samples generates additional phases. The parameters of the Mössbauer spectra depend on the zinc concentration. In this case, for pure bismuth ferrite, the spectrum is a superposition between two Zeeman sextets and two paramagnetic doublets arising from two nonequivalent magnetic and electrical positions occupied by iron ions at the crystallattice sites of a sample. The replacement of iron ions with zinc ions substantially affects the spectrum parameters. This is probably related to changes in the spin-cycloid structure typical of multiferroics, the destruction of which stimulates the appearance of significant magnetoelectric interactions.     

Study of domain structure of magnetic powder particles by Mössbauer spectroscopy

The determination technique of monodomain state of the magnetic powder particles using the Mössbauer spectroscopy is described. The method was verified on the particles of gadolinium iron garnet near the compensation temperature. It has also shown that using the Mössbauer spectroscopy we can evaluate the domain wall energy in ferrites possessing the compensation point.     

Enthalpies of solvation of ethylene oxide oligomers CH3O(CH2CH2O)nCH3 (n = 1 to 4) in different H-bonding solvents: Methanol, chloroform, and water. Group contribution method as applied to the polar oligomers

The enthalpies of solution and solvation of ethylene oxide oligomers CH₃O(CH₂CH₂O)_nCH₃ (n = 1 to 4) in methanol and chloroform have been determined from calorimetric measurements at T = 298.15 K. The enthalpic coefficients of pairwise solute–solute interaction for methanol solutions have been calculated. The enthalpic characteristics of the oligomers in methanol, chloroform, water and tetrachloromethane have been compared. The hydrogen bonding of the oligomers with chloroform and water molecules is exhibited in the values of solvation enthalpy and coefficient of solute–solute interaction. This effect is not observed for methanol solvent. The thermochemical data evidence an existence of multi-centred hydrogen bonds in associates of polyethers with the solvent molecules. Enthalpies of hydrogen bonding of the oligomers with chloroform and water have been estimated. The additivity scheme has been developed to describe the enthalpies of solvation of ethylene oxide oligomers, unbranched monoethers and n-alkanes in chloroform, methanol, water, and tetrachloromethane. The correction parameters for contribution of repeated polar groups and correction term for methoxy-compounds have been introduced. The obtained group contributions permit to describe the enthalpies of solvation of unbranched monoethers and ethylene oxide oligomers in the solvents with standard deviation up to 0.6 kJ · mol⁻¹. The values of group contributions and corrections are strongly influenced by solvent properties.     

Enthalpies of solvation of macrocyclic ether of dibenzo-24-crown-8 in solvents of different polarity

Enthalpies of solution of dibenzo-24-crown-8 in tetrachlormethane, benzene, chloroform, pyridine, acetone, acetonitrile, DMF, DMSO and propylene carbonate have been determined by calorimetric method at 298.15 K. The changes in enthalpy of solute-solvent interaction for the transfer the ether from inert tetrachlormethane into various solvents have been calculated from the obtained data. The thermochemical characteristics obtained for dibenzo-24-crown-8 have been compared with similar ones for dibenzo-18-crown-6 having a smaller cycle size. It has been found that an exothermicity of solute-solvent interaction changes to a lesser extent for transfer of the larger cyclic ether into polar solvents. But the effect increases more sharply for the transfer to chloroform. It has been concluded that the contribution from electrostatic interaction with solvent decreases with an increase of the cycle size as result of the increasing structural flexibility and decreasing polarity of cycle. But the contribution from hydrogen bonding with chloroform becomes larger due to an increase in the number of donor atoms of the ether molecules. It was ascertained that the ability to bind specifically acetonitrile molecules disappears in going from 18-merous to 24-merous cycle.     

Mössbauer studies of the spectra of <Superscript>57</Superscript>Fe nuclei in Late Cenozoic endogenous formations of the Eastern Caucasus

Three types of manifestations of Late Cenozoic endogenous activity (pyroclastic, hydrothermal explosive, and volcanogenic sedimentary formations) have been found over the last decade in different geostructural zones of the Terek–Caspian foretrough and the Alpine fold–thrust structure in the Eastern Caucasus. The results from Mössbauer studies show that these formations contain fractions of iron and its compounds with complex crystal structures in which ⁵⁷Fe atoms occupy nonequivalent positions in the lattice with respect to their magnetic and electric fields, exist in different physicochemical states, and occur in various phases of the endogenous process products.     

X-ray dosimetric characteristics of CdIn2S4〈Cu〉 single crystals

The effect of doping CdIn₂S₄ single crystals by copper (3 mol %) on their X-ray dosimetric characteristics is investigated. It is found that the characteristic X-ray conductivity of CdIn₂S₄〈Cu〉 single crystals increases 3–16 times compared with undoped CdIn₂S₄ at effective radiation hardness V _a = 25−50 keV and dose rate E = 0.75−78.05 R/min. Moreover, the persistence of the crystal characteristics completely disappears and the supply voltage of a CdIn₂S₄〈Cu〉 X-ray detector decreases fivefold. The dependence of the steady X-ray-induced current in CdIn₂S₄〈Cu〉 on the X-ray dose is described as ΔI _{E, 0} ∝ E ^α, where 0.6 ≤ α ≤ 1.8.     

Effect of solvent media and condensed benzene rings on thermochemical behaviour of dibenzo-18-crown-6 in solution

The specific and non-specific interactions of twelve activated carbon cloth samples prepared from commercial cotton fabric, and that present different activation degrees are studied through the determination of immersion enthalpies in CCl₄ and H₂O, and in aqueous solutions of NaOH and HCl. The immersion enthalpies found for the solvents CCl₄ and H₂O are in a range of 5.49–45.84 and 1.77–7.76 J g⁻¹, respectively. The enthalpic values for the materials in aqueous solutions of NaOH and HCl, allow characterizing the chemical surface of these materials, which are in a range of 6.63 and 21.49 J g⁻¹, finding through them important relations in company with other characterizing techniques used in the study of these materials.