Том 81, № 7 (2017)

Two samples with immobilized magnetic nanoparticles are synthesized and investigated. The first sample has randomly oriented easy axes of magnetic anisotropy; the second sample has preferentially aligned easy axes, produced via the precipitation of a colloid of ferromagnetic particles in the presence of a magnetic field. It is shown that the precipitation of an aqueous suspension of nanoparticles in the presence of a magnetic field greatly changes the anisotropy of a sample, compared to one prepared by precipitation without a magnetic field. The second sample exhibits a preferential direction of the easy axes of magnetic anisotropy that coincides with the direction of the external magnetic field applied in the drying process of sample preparation.

A hypothesis based on the literature data on the Mössbauer, structural, and magnetic parameters of different iron oxidation states is proposed, according to which changes in the electronic configuration of an iron ion that are caused by an electron (or a change of iron oxidation state by one) can vary the isomer shift by a constant (~0.33 mm s⁻¹), if it is assumed that the structure of the iron’s valent shell and iron spatial environment remain unchanged.

A completely austenitic structure has been obtained ten times faster via the mechanical alloying (MA) of high-nitrogen 25Cr10Mn1N alloy from metal components and manganese nitride than during the MA of similar steels in a nitrogen atmosphere. A mechanism for the bcc → fcc phase transformation that occurs during MA, and where deformation stacking faults of the layer fault type on the {211} atomic planes of the bcc phase play a key role, is considered and proposed.

Phase transitions in aqueous films adsorbed in clays are studied and reported for the first time. Analysis of spectral parameters allows the orto/spin-isomer pair ratio in frozen water to be established, and the Mössbauer probes to be localized on the alumosilicate surface. The temperature transformation of the spectra is explained using models that qualitatively describe first- and second-order phase transitions.

The Mössbauer effect is used to study changes in the structure of Fe₅₀Pd₅₀ alloy in the course of annealing for ordering at T = 450°C from different initial states: cast and quenched from 950°C, then subjected to severe plastic deformation by shear under pressure, and that obtained by fast quenching from the melt. Differences in the kinetics of phase transformations are observed depending on the initial state of the material.

Iron and iron–cobalt nanostructures are probed by means of Mössbauer spectroscopy combined with scanning electron microscopy, energy-dispersion analysis, and X-ray diffraction. The obtained nanostructures are single-phase Fe_{1 − x}Co_x (0 ≤ x ≤ 1) nanotubes that have high degrees of polycrystallinity and a bcc lattice 12 μm long and 110 ± 3 nm in diameter, with walls 21 ± 2 nm thick. A random distribution of the orientations of the magnetic momenta of Fe atoms are observed for Fe nanotubes, while Fe–Co nanotubes are characterized by a magnetic texture along their axes.

Deformation-induced iron and manganese atomic separation in a bcc solid solution is detected via Mössbauer spectroscopy in Fe_93.2Mn_6.8 alloy after high pressure torsion deformation in Bridgman anvils. The rate of short-range separation grows along with the temperature of deformation.

A universal approach to describing the equilibrium magnetization curves and relaxation Mössbauer spectra of magnetic nanoparticles is proposed for consistent analysis of magnetometry and gamma-resonance experimental data, based solving a quantum-mechanical problem for a particle with spin S that has intrinsic magnetic anisotropy and is positioned in an external magnetic field.

The applicability of Mössbauer spectroscopy in studying grain boundaries in ultrafine-grained materials produced by severe plastic deformation (SPD) is analyzed. It is shown that grain boundaries after SPD are in a nonequilibrium state that is characterized by excess free volume.

New La/Zn substituted strontium ferrites Sr_{(2 −x)}La_x[Fe_{(2 − x)}Zn_x]O₅, (0 ≤ x ≤ 0.3) with brownmillerite- type structure are obtained and studied via X-ray phase analysis and Mössbauer spectroscopy. Depending on the conditions of synthesis, substituting Zn²⁺ cations can either mainly occupy tetrahedral positions in a brownmillerite structure, or be uniformly distributed between the tetrahedral and octahedral positions. It is shown that they are reversibly oxidized by atmospheric oxygen at elevated temperatures.

A model of frequency and time-domain Mössbauer forward scattering (FS) spectra on a magnetic target in the regime of RF hyperfine field reversals is proposed. The model allows us to describe the temperature dependence of RF effects in the FS frequency spectra of FeBO₃ measured at temperatures below the Néel point (~348 K). In the proposed model, temporal (with internal mark) Mössbauer FS spectra on a magnetic target are calculated to study the dependence of the structure of these spectra on the target’s optical thickness, the degree of phase correlation of the RF hyperfine field reversals, and the value of the phase of the RF field used as an external parameter.

A synthesis procedure that allows us to obtain ZnO:0.3 at % ¹¹⁹Sn samples with Sn²⁺ ions on the surfaces of oxide particles containing structure-forming cations on tetrahedral sites is developed for the first time. Analysis of the ¹¹⁹Sn Mössbauer spectra of obtained samples does not confirm the existence of the localized magnetic moments at ZnO grain boundaries recently suggested in the literature.

Samples of biogenic iron minerals obtained during the growth of the anaerobic alkaliphilic ironreducing bacterium Fuchsiella ferrireducens (strain Ζ-7101^Т) in the presence of synthesized ferrihydrite used as electron acceptor are studied by ⁵⁷Fe Mössbauer spectroscopy. Two series of samples, differing by electron acceptor, are analyzed. Ethanol and acetate are used as electron donors in the first and second series, respectively. Mössbauer studies are performed at room temperature and at 82 K. Phases containing ferrous iron (siderite) form in both series, while a magnetically ordered phase (a mixture of hematite and maghemite particles) forms only in the series with ethanol.

Using sufficiently accurate uniform analytical approximations (applicable for all physically significant values of depths, zenith angles, and energies) of solutions to the equations of a simple model of a nuclear cascade in the atmosphere, formulas for the fluxes of mesons and muons for all depths (above sea level), energies, and zenith angles are derived.