The effect of substitutional 4f-elements on the magnetism of rare-earth compounds RFe2-type with the Laves phase structure is studied to find new multifunctional materials, as well as to define the macro- and microscopic parameters of multicomponent magnets. The crystal structure of (Er,Y,Sm)Fe2 compounds is investigated by X-ray powder diffraction. Detailed information on the magnetic properties of the iron sublattice for multicomponent compounds with three different rare-earth elements is obtained for the first time by means of the 57Fe Mössbauer spectroscopy. The main regularities in the magnitude variation of magnetocaloric effect and magnetostriction (linear, anisotropic and volume) in varying composition of the (Er,Y,Sm)Fe2 compounds are determined.

In this paper, we studied substituted lanthanum orthoferrite La 0.67 Sr 0.33 FeO 3 – γ by Mössbauer spectroscopy using X-ray diffraction data. A series of vacuum annealings was performed in the temperature range of t ann = 200–650°C, after which no significant changes in the structure of the samples were detected. The Mössbauer measurements at room temperature show that the Fe ions are in an average valence state between Fe 3+ and Fe 4+ . Upon vacuum annealing, as the temperature t ann increased, the average hyperfine magnetic field on the 57 Fe nuclei and the isomer shift of the spectrum increased, which is associated with an increase in the number of vacancies and, accordingly, a decrease in the amount of Fe 4+ . Mössbauer measurements at 85 K showed that the average valence state of iron does not manifest itself. The hyperfine parameters of the low-temperature Mössbauer subspectra obtained from the model interpretation indicate that one of them belongs to Fe 4+ ions, and the rest belong to Fe 3+ . The presence in the spectra of several sextets related to Fe 3+ ions is due to the appearance of oxygen vacancies (breaking of the Fe 3+ –O 2– –Fe exchange bond) and Fe 4+ ions (weakening of the Fe 3+ –O 2– –Fe exchange bond) in the nearest ionic neighborhood of Fe atoms. Both factors cause a decrease in the hyperfine magnetic field and a change in the isomer shift of the spectrum. As a result of model interpretation of the Mössbauer spectra, the numbers of oxygen vacancies and Fe 4+ ions per formula unit depending on vacuum annealing temperature t ann were determined for all samples. It was shown that at t ann above 450°C, the process of oxygen leaving the lattice ends and only Fe 3+ ions are detected.

The valence states of Fe atoms and the formation of oxygen vacancies in substituted La0.67Sr0.33FeO3−γ orthoferrite have been studied in detail by low-temperature Mössbauer spectroscopy under oxygen removal. It has been shown that the averaged valence state of Fe atoms is not revealed with a decreasing measurement temperature. This makes it possible to reveal Fe4+ ions. The Analysis of the obtained data allows us to conclude that the presence of several Zeeman sextets associated with Fe3+ ions is related to the appearance of oxygen vacancies and Fe4+ ions in the nearest ionic surrounding of Fe ions. Using the Mössbauer data, the number of oxygen vacancies and oxygen ions has been determined for all the studied samples depending on the vacuum annealing temperature.

The valence states of Fe atoms and the formation of oxygen vacancies in substituted La 0.67 Sr 0.33 FeO 3-γ orthoferrite have been studied in detail by low-temperature Mossbauer spectroscopy under oxygen removal. It has been shown that the averaged valence state of Fe atoms is not revealed with a decreasing measurement temperature. This makes it possible to reveal Fe 4+ ions. The Analysis of the obtained data allows us to conclude that the presence of several Zeeman sextets associated with Fe 3+ ions is related to the appearance of oxygen vacancies and Fe 4+ ions in the nearest ionic surrounding of Fe ions. Using the Mossbauer data, the number of oxygen vacancies and oxygen ions has been determined for all the studied samples depending on the vacuum annealing temperature. Keywords: perovskites, substituted lanthanum ferrites, X-ray diffraction analysis, Mossbauer spectroscopy, Fe valence states, oxygen vacancies.

Magnetic and Mössbauer measurements are performed on the nuclei of 57 Fe probe atoms in the structure of the substituted CaCu x Mn 6.96 – x 57 Fe 0.04 O 12 (0 ≤ x ≤ 1) manganites in the magnetic-ordering temperature range T ≤ T N,C . The experimental results are used to analyze the exchange interactions and the possible magnetic-ordering configurations of cations with octahedral (Mn 3+ /Mn 4+ ) and square (Cu 2+ /Mn 3+ ) oxygen coordinations. The causes of the nonmonotonic change in the magnetic-ordering temperature T N,C ( x ) with composition x of the copper-substituted manganites are considered.

Mössbauer studies of the anisotropy of hyperfine interactions (HFIs) of the 57Fe nuclei in the quasi-binary intermetallic system Zr1 –xScxFe2 (0 ≤ x ≤ 1) with the structure of the cubic Laves phase of the C15 type have been performed. Within the framework of the tensor description of the anisotropy of magnetic HFIs, taking the crystal and magnetic structure into account, the hyperfine parameters of the partial spectra have been expressed through the constant of the quadrupole interaction, the isotropic and anisotropic magnetic fields, and also the azimuthal and polar angles, which specify the orientation of the direction of the easy axis of magnetization (EA). It has been established that at temperatures of 87 and 297 K the EA deviates in the plane $$(1\bar {1}0)$$ from the crystallographic direction [111] by ~15°, and with an increase in the concentration x, the orientation of the EA almost does not change. The changes in the isotropic field and in the shift of the Mössbauer line have an anomalous character. With an increase in x, an increase can first be observed, and then, at x > 0.4, a decrease of the magnitude of the isotropic field can be observed. The shift of the Mössbauer line decreases with an increase in x; at x ~ 0.4, a bent is observed. This anomalous behavior of the isotropic field and of the shift correlates with a change in the lattice parameter and in the magnetic moment of the Fe atoms. The anisotropic field decreases linearly with an increase in the concentration of Sc atoms, while the constant of the quadrupole interaction almost does not change, ~1 mm/s.

We present the results of our 57Fe probe Mössbauer study in manganites CaCuxMn6.96–x57Fe0.04O12 (0 ≤ x ≤ 1). We have established that for compositions 0 ≤ x ≤ 0.15 near the structural R$$\bar {3}$$ ↔ Im$$\bar {3}$$ transition (at T ≈ TCO), an increase in the temperature leads to a decrease in the content of the rhombohedral phase (R$$\bar {3}$$) against a background of the “nucleation” and gradual increase in the fraction of the cubic phase (Im$$\bar {3}$$), in which all octahedral positions of manganese are equivalent due to the electron exchange Mn3+ ↔ Mn4+. The increase in the electron exchange frequency is assumed to be related to a weakening of the electron–lattice interaction of Jahn–Teller Mn3+ cations as x → 0.4. An increase in the copper content leads to a sharp decrease in the phase transition temperature TCO. A single component corresponding to the cubic phase (Im$$\bar {3}$$) is present in the spectrum starting from x ≥ 0.4. Based on our Mössbauer data, we have constructed a T–x phase diagram.

Mössbauer studies of the anisotropy of hyperfine interactions (HFIs) of the 57 Fe nuclei in the quasi-binary intermetallic system Zr 1 – x Sc x Fe 2 (0 ≤ x ≤ 1) with the structure of the cubic Laves phase of the C15 type have been performed. Within the framework of the tensor description of the anisotropy of magnetic HFIs, taking the crystal and magnetic structure into account, the hyperfine parameters of the partial spectra have been expressed through the constant of the quadrupole interaction, the isotropic and anisotropic magnetic fields, and also the azimuthal and polar angles, which specify the orientation of the direction of the easy axis of magnetization (EA). It has been established that at temperatures of 87 and 297 K the EA deviates in the plane (11̅0) from the crystallographic direction [111] by 15°, and with an increase in the concentration x , the orientation of the EA almost does not change. The changes in the isotropic field and in the shift of the Mössbauer line have an anomalous character. With an increase in x , an increase can first be observed, and then, at x > 0.4, a decrease of the magnitude of the isotropic field can be observed. The shift of the Mössbauer line decreases with an increase in x ; at x 0.4, a bent is observed. This anomalous behavior of the isotropic field and of the shift correlates with a change in the lattice parameter and in the magnetic moment of the Fe atoms. The anisotropic field decreases linearly with an increase in the concentration of Sc atoms, while the constant of the quadrupole interaction almost does not change, 1 mm/s.

Представлены результаты мёссбауэровских исследований на ядрах 57Fe в мультиферроике BiFeO3 в диапазоне температур, включающем температуру магнитного фазового перехода. Обработка и анализ мёссбауэровских спектров проводили методами восстановления распределений сверхтонких магнитных полей и расшифровки в модели пространственной спин-модулированной структуры циклоидного типа. Получены температурные зависимости сверхтонких параметров спектра – сдвига и квадрупольного смещения мёссбауэровской линии, изотропного и анизотропного вкладов в сверхтонкое магнитное поле, а также параметра ангармонизма несоразмерной спиновой волны.

The results from 57 Fe Mössbauer spectroscopic studies of multiferroic BiFeO 3 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.

Mossbauer and X-ray diffraction studies of nanocomposites based on iron oxides and pectin (PC) were carried out involving magnetization measurements. The concentrations of PC in nanocomposites varied from 0 to 10%. Mossbauer investigations of nanocomposites were carried out in the temperature range from 5 to 300 K. Many-state superparamagnetic relaxation model was used for spectra fitting. The magnetization, M(T,H), was measured in the temperature interval of 80-300 K and magnetic field up to 10 kOe. Formation of the "iron-polymer" interface was not observed. Particle sizes were estimated using the Mossbauer and X-ray powder diffraction data.

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.

Nanocomposites containing iron oxides and humic acids were studied by Mössbauer and magnetic measurements. The concentrations of humic acids as the precursor in nanocomposites were varied. Mössbauer investigations were carried out at temperature range from room temperature to 5 K. The magnetization M(T, H) was measured in the temperature interval 80–300 K and magnetic field up to 10 kOe. It was found that particles of investigated nanocomposites exhibit superparamagnetic properties. The core of the nanocomposite was a mixture of non-stoichiometric magnetite and maghemite. The “iron-polymer” interface was formed on the surface of the iron oxide particles.

The hyperfine magnetic interactions of 119Sn probe atoms in the CaCu3Mn3.96Sn0.04O12 double manganite by Mössbauer spectroscopy using magnetic measurements have been investigated. A consistent description of the results obtained in terms of the Weiss molecular field model by taking into account the peculiarities of the local environment of tin atoms has allowed the indirect Cu2+OMn4+ (JCuMn 51 ± 1 K) and Mn4+OMn4+ (JMnMn 0.6 ± 0.6 K) exchange interaction integrals to be estimated. Based on the KanamoriGoodenoughAnderson model, we show that the magnitude and sign of the intrasublattice exchange integral JMnMn correspond to both the electronic configuration of the Mn4+ cations and the geometry of their local crystallographic environment in the compound under study.

The double manganite CaCu${}_{3}$Mn${}_{4}$O${}_{12}$ doped with ${}^{119}$Sn atoms (\ensuremath{\sim}1 at.$%$ with respect to manganese atoms) was studied by use of M\"ossbauer spectroscopy. Formally tetravalent Sn${}^{4+}$ ions substitute for isovalent manganese ions in the octahedral (Mn${}^{4+}$O${}_{6}$) polyhedra. The covalency effects on the magnetic interactions like superexchange in Cu${}^{2+}$-O-Mn${}^{4+}$ and Mn${}^{4+}$-O-Mn${}^{4+}$ bonds and supertransferred hyperfine interactions of the ${}^{119}$Sn probe atoms in the manganite structure are discussed. Using a semiquantitative nearest-neighbor cluster model relating the hyperfine magnetic field on the ${}^{119}$Sn nuclei (${H}_{\mathrm{Sn}}$ $=$ 105 kOe at $T$ $=$ 77 K) to covalency parameters and angle characterizing the Sn-O-$M$ ($M$ $=$ Cu, Mn) bonds, it has been shown how such an analysis of supertransferred hyperfine interactions of tin probe ions can get fruitful information about strength and sign of the superexchange interactions between Mn${}^{4+}$ and Cu${}^{2+}$ magnetic ions. A consistent description of the results in the framework of the Weiss molecular field model considering the specific local environment of tin atoms has made it possible to estimate exchange integrals: ${J}_{\mathrm{CuMn}}$ $=$ \ensuremath{-}51.1 \ifmmode\pm\else\textpm\fi{} 0.3 K and ${J}_{\mathrm{MnMn}}$ $=$ \ensuremath{-}0.6 \ifmmode\pm\else\textpm\fi{} 0.2 K.