M. E. Matsnev

Study of spatial spin-modulated structures by Mössbauer spectroscopy using SpectrRelax

SpectrRelax is an application for analysis and fitting of absorption and emission Mossbauer spectra. It includes a large selection of static and relaxation spectrum models, and allows fitting and searching for optimal model parameters. Recently, we have added new models for Mossbauer spectra of nuclides in spatial spin modulated structures. In these structures, spin density or direction changes in a periodic way along a single direction, and this wave is incommensurate with the underlying lattice. The models include Spin/Charge density wave, where the shape of this wave is represented as a sum of odd harmonics, Anharmonic spin modulation where the spin direction has a cycloidal type modulation, and a Spiral-like spin structure, in which magnetic moments rotate in a plane perpendicular to the wave propagation vector, forming a spiral.

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.

Mössbauer investigations of hyperfine interactions features of 57Fe nuclei in BiFeO3 ferrite

New results of 57Fe Mossbauer studies on BiFeO3 powder sample performed at various temperatures above and below magnetic phase transitions point TN ≈ 640K are reported. We have performed self-consistent calculations of the lattice contributions to the EFG tensor, taking into account dipole moments of the O2− and Bi3+ ions. Low-temperature 57Fe Mossbauer spectra recorded at T < TN were analyzed assuming an anharmonic cycloidal modulation of the Fe3+ magnetic moments. The cycloidal modulation of the iron spin was described with the elliptic Jacobi function sn[(±4K(m)/λ)x,m]. The good fit of the experimental spectra was obtained for the anharmonicity m = 0.44 ± 0.04 (T = 4.9K) resulting from the easy-axis magnetic anisotropy.

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.

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.

Mössbauer studies of BiFe1–xScxO3 (x = 0, 0.05) Multiferroics

The effect replacing Fe atoms with Sc atoms has on the spatial spin-modulated structure and electrical and magnetic hyperfine interactions of 57Fe nuclei in BiFeO3 multiferroic is studied by means of Mössbauer spectroscopy. The temperature dependences of the parameter of anharmonicity and hyperfine parameters of the Mössbauer spectrum of 57Fe nuclei are obtained for all of the investigated ferrites in the temperature range of 5–300 K.

Analysis of the Magnetic Structure of the BiFeO3 Multiferroic by Mössbauer Spectroscopy

Specific features of the magnetic structure of the BiFeO3 multiferroic have been investigated by Mössbauer spectroscopy in the temperature range of 150–450 K. The temperature dependence of the anharmonicity parameter of the cycloidal spatial spin-modulated structure has been measured, and the magnetic anisotropy constant has been estimated.

Mössbauer studies of spatial spin-modulated structure and hyperfine interactions in multiferroic Bi57Fe0.10Fe0.85Cr0.05O3

Results of Mössbauer investigations on 57Fe nuclei in multiferroic material Bi57Fe0.10Fe0.85Cr0.05O3 in the temperature range from 5.2 to 300 K are presented. Bulk rhombohedral samples were obtained by solidstate synthesis at high pressure. Mössbauer spectra were analyzed using the model of spatial incommensurate spin-modulated structure of the cycloidal type. Information on the influence of substituting Cr cations for Fe cations on hyperfine spectral parameters was obtained: the shift and quadrupolar shift of a Mössbauer line, and isotropic and anisotropic contributions into the hyperfine magnetic field. The anharmonicity parameter m of the spatial spin-modulated structure increases almost 1.7 times at 5.2 K when BiFeO3 is doped with chromium. The data on m were used for calculation of the uniaxial magnetic anisotropy constants and their temperature dependences for pure and chromium-doped BiFeO3.

Spatial spin-modulated structure and hyperfine interactions of 57Fe nuclei in multiferroics BiFe1–xTxO3 (T = Sc, Mn; x = 0, 0.05)

The results of the Mössbauer studies on 57Fe nuclei in multiferroics BiFe1–xTxO3 (T = Sc, Mn; x = 0, 0.05) in the temperature range of 5.2–300 K have been presented. The Mössbauer spectra have been analyzed in terms of the model of an incommensurate spatial spin-modulated structure of cycloid type. Information has been obtained about the effect of the substitution of Sc and Mn atoms for Fe atoms on the hyperfine parameters of the spectrum: the shift and the quadrupole shift of the Mössbauer line, the isotropic and anisotropic contributions to the hyperfine magnetic field, and also the parameter of anharmonicity of the spatial spin-modulated structure.

Specific Features of Magnetic States of Impurity Iron Ions in the Perovskite La0.75Sr0.25Co0.9857Fe0.02O3

Single-phase polycrystalline La0.75Sr0.25Co0.9857Fe0.02O3 samples have been prepared by solidstate ceramic technology. The samples have the rhombohedral structure (space group