V. S. Rusakov

Diagnostics of a spatial spin-modulated structure using nuclear magnetic resonance and Mössbauer spectroscopy

Methods of the diagnostics of the spatial spin-modulated structure of the cycloidal type in multiferroics based on nuclear magnetic resonance and Mössbauer spectroscopy have been considered. It has been established that Mössbauer spectroscopy makes it possible to determine the anharmonicity parameter of the spatial spin-modulated structure of the cycloidal type with no worse accuracy than nuclear magnetic resonance with higher resolution. Mössbauer spectroscopy, being sensitive to the hyperfine quadrupole interaction of the nucleus in the excited state, makes it possible to obtain additional information on the features of the spatial spin-modulated structure.

Structure and physical properties of iron nanotubes obtained by template synthesis

Iron nanotubes with an aspect ratio of approximately 100 are synthesized by electrochemical deposition using polyethylene terephthalate templates. The structural and morphological features of the nanotubes are studied in detail by scanning electron microscopy, energy dispersive analysis, transmission electron microscopy, electron diffraction, X-ray diffraction analysis, and gas permeability. The main magnetic parameters and their dependence on temperature are determined by vibration magnetometry and Mössbauer spectroscopy.

Spatially modulated magnetic structure of AgFeO2: Mössbauer study on 57Fe nuclei

The results of the Mössbauer study of ferrite AgFeO2 manifesting multiferroic properties (at T ≤ TN2) have been presented. The hyperfine interaction parameters of 57Fe nuclei have been analyzed in a wide temperature range including the points of two magnetic phase transitions (TN2 ≈ 7–9 K and TN1 ≈ 15–16 K). It has been shown that the Mössbauer spectra of the 57Fe nuclei are sensitive to the variations of the character of the magnetic ordering of Fe3+ ions in the studied ferrite. The results of the model identification of a series of spectra (4.7 K ≤ T ≤ TN2) under the assumption of the cycloid magnetic structure of ferrite AgFeO2 have been presented. The analysis of the results has been performed in comparison with the literature data for other oxide multiferroics.

Local structure, chemical bond parameters and hyperfine magnetic interactions of 57Fe and doped 119Sn atoms in the orthoferrites TlFeO3 and TlFe0.99Sn0.01O3

M?ssbauer spectroscopy has been applied to study the magnetic hyperfine interactions of 57Fe and 119Sn probe atoms within TlFeO3 and TlFe0.99Sn0.01O3 ferrites. According to the magnetic measurements, the magnetic ordering temperature TN (= 560?K) for TlFeO3 is much lower than that for any other orthoferrites RFeO3 (R = rare earth). It is suggested that such difference in TN may be explained by different characteristics of the Tl?O and R?O chemical bonds involved and the induced competition with the Fe?O bonds. The effects of covalency and overlap distortion on the spin and charge densities at 57Fe nuclei are discussed in relation with the hyperfine interactions observed. By using cluster molecular orbital (MO) calculations, it was shown that the low value of the hyperfine magnetic field HFe(= 538?kOe) at 57Fe nuclei in TlFeO3 is strongly associated with a decrease of the covalent mixing parameter (b?)2 = 0.048 and (b?)2 = 0.009 values, which characterize the Fe?O bond covalence. It was elucidated that the value of super-transferred hyperfine field (HSTHF) at 119Sn nuclei in TlFe0.99Sn0.01O3 is sensitive mainly to the angle of the Sn?O?Fe bonds.

Mössbauer study of formation of iron oxides and carbonate by dissimilatory alkaliphilic bacterium

The process of amorphous Fe(III)-hydroxide (AFH) reduction by anaerobic alkaliphilic bacterium – Geoalkalibacter ferrihydriticus (strain Z-0531) was investigated by Mossbauer spectroscopy methods. Strain Z-0531 was isolated from the sediments of soda Lake Khadyn (Tuva, Russian Federation). The influence of AFH concentration and the concentration of anthraquinone-2,6-disulfonate added to the cultivation medium as well as the incubation time influence on the reducing process were studied. It was found that increase in the time of cultivation of bacteria led to an increase in the relative content of phases containing ferrous atoms that could be explained by the adaptation of bacterium to the cultivation medium.

Mössbauer study of compounds of Cu3 − xFexSnS4 and Cu2Fe1 −xZnxSnS4 systems

A Mössbauer study of the structural and charge states of 57Fe and 119Sn atoms in the compounds of Cu3 −xFexSnS4 and Cu2Fe1 − xZnxSnS4 systems was performed. It was shown that the iron atoms in the compounds of both systems were in the divalent and trivalent states occupying the tetrahedral positions of the structure. The character of the changes of the degree of covalency of the Fe2+-S, Fe3+-S and Sn4+-S bonds during the isomorphic substitution in the systems was established.

Mössbauer Investigation of Biologically-Induced Mineralization Processes

Mossbauer investigations of the kinetics of iron-containing mineral formation in controlled conditions by thermophilic Fe(III)-reducing bacteria were carried out. Anaerobic bacterium (strain Z-0001) was isolated from the ferric sediments of hot springs Stolbovskie, Kunashir Island. This microorganism used the amorphous Fe(III)-oxide as an electron acceptor and acetate CH3COO− as an electron donor. Probes of solid phase processed by bacteria were sampled at different time intervals for the cultures incubated with 20 and 100% of CO2 in gas phase and studied by Mossbauer spectroscopy. The influence of physical and chemical conditions on the mineral phase formation was also investigated.

Mössbauer study of isomorphous substitutions in Cu2Fe1-xCuxSnS4 and Cu2Fe1-xZnxSnS4 series

The investigation of isomorphous substitutions in minerals of stannite group was carried out for two series Cu2FeSnS4 – Cu3SnS4 (stannite – kuramite) and Cu2FeSnS4 – Cu2ZnSnS4 (stannite – kesterite) by 57Fe and 119Sn Mossbauer spectroscopy. The calculation of the lattice contribution to the electric field gradient tensor at the 57Fe nuclei and an estimation of the quadrupole shift for the determination of Fe3+ atom positions in the structure were carried out. The charge and structural states of Fe and Sn atoms in compounds of the two systems were determined. The schemes of isomorphous substitutions were found for both series in all range of iron concentrations. The changes in the covalence degree of the bonds Fe2+ − S, Fe3+ − S and Sn4+ − S in the process of the substitution were found.

Structure of the local environment and hyperfine interactions of 57Fe probe atoms in DyNiO3 nickelate

The local structure of DyNiO3 nickelate at both sides of the insulator (T < Tim) ↔ metal (T > Tim) phase transition was studied by probe 57Fe Mössbauer spectroscopy. The character of change in the hyperfine parameters of probe iron atoms specifically near the phase-transition temperature (T ≈ Tim) was analyzed.

Temperature investigations of the spatial spin-modulated structure of multiferroic BiFeO3 by means of Mössbauer spectroscopy

The results from 57Fe Mössbauer spectroscopic studies of multiferroic BiFeO3 in a range of tem-peratures including that of the magnetic phase transition are presented. The Mössbauer spectra are processed and analyzed by reconstructing the hyperfine magnetic field distributions and interpreting the spectra with a cycloid-type spatial spin-modulated structure model. The temperature dependences of the hyperfine spectrum parameters (the Mössbauer line shift, the quadrupole shift, and the isotropic and anisotropic contributions to the hyperfine magnetic field) are obtained, along with the anharmonicity parameter of an incommensurate spin wave.