Belarussian State Agrarian Technical University

Minsk, Belarus

Belarussian State Agrarian Technical University

Minsk, Belarus
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Troyanchuk I.O.,National Academy of Sciences of Belarus | Bushinskii M.V.,National Academy of Sciences of Belarus | Chobot A.N.,National Academy of Sciences of Belarus | Tereshko N.V.,National Academy of Sciences of Belarus | And 4 more authors.
Physics of the Solid State | Year: 2017

The system of La1–xSrxCo0.5Mn0.5O3 solid solutions have been studied by neutron diffraction and the measurement of the magnetization. The composition with x = 0 has the monoclinic structure (space group P21/n); the compositions with 0.15 ≤ x ≤ 0.6 are rhombohedral (R3 ¯ c), and the composition with x = 0.75 is cubic (Pm3 ¯ m). All the compositions with x ≤ 0.75 are shown to contain a ferromagnetic component. The stoichiometric composition with x = 0.5 undergoes a sharp ferrromagnet–paramagnet transition at 240 K; however, no coherent magnetic contribution to the neutron diffraction has been detected. The magnetic data are interpreted, assuming that the ferromagnetism at x ≤ 0.15 is due to positive superexchange Co2+–O–Mn4+ interaction, while, at x ≥ 0.25, the superexchange interaction between ions Co3+ in a high-spin state and ions Mn4+ is responsible for the ferromagnetic component. © 2017, Pleiades Publishing, Ltd.


Dobryansky V.M.,Belarussian State Agrarian Technical University | Tobbens D.M.,Helmholtz Center Berlin | Sikolenko V.,Helmholtz Center Berlin | Sikolenko V.,Joint Institute for Nuclear Research | Efimov V.,Joint Institute for Nuclear Research
Journal of Magnetism and Magnetic Materials | Year: 2015

Abstract Magnetic properties and crystal structure of La0.7Sr0.3Mn1-xMexO3 (Me=Ga, Fe, Cr; x≤0.3) have been studied by neutron powder diffraction and magnetization measurements. It is shown that substitution of manganese ions by chromium or gallium ions (x=0.3) leads to phase separation into antiferromagnetic and ferromagnetic phases whereas replacement by Fe ions stabilizes spin glass state (x=0.3). Ferromagnetic interactions in Cr-substituted compounds are much more pronounced than in Fe- and Ga-doped ones. Magnetic properties are discussed in the model assuming a dominance of superexchange interactions. It is considered that ferromagnetism in the Cr-substituted compositions is associated with nearly equal contributions from positive and negative components of the superexchange interaction between Mn3+ and Cr3+ ions as well as to mixed valence of chromium ions. The spin glass state observed for the Fe-doped sample (x=0.3) is associated with strong antiferromagnetic superexchange between Fe3+-O-Fe3+ and Fe3+-O-(Mn3+, Mn4+). © 2015 Elsevier B.V.


Henchy C.,National University of Ireland, Maynooth | McCaffrey J.G.,National University of Ireland, Maynooth | Arabei S.,Belarussian State Agrarian Technical University | Pavich T.,B. I. Stepanov Institute of Physics | And 3 more authors.
Journal of Chemical Physics | Year: 2014

The absorption, fluorescence, and excitation spectra of free base tetraazaporphine (H2TAP) trapped in Ne, N2, and Ar matrices have been recorded at cryogenic temperatures. Normal Raman spectra of H2TAP were recorded in KBr discs and predicted with density functional theory (DFT) using large basis sets calculations. The vibrational frequencies observed in the Raman Spectrum exhibit reasonable agreement with those deduced from the emission spectra, as well as with frequencies predicted from large basis set DFT computations. The upper state vibrational frequencies, obtained from highly resolved, site selected excitation spectra, are consistently lower than the ground state frequencies. This contrasts with the situation in free base phthalocyanine, where the upper state shows little changes in vibrational frequencies and geometry when compared with the ground state. Investigations of the photochemical properties of H2TAP isolated in the three matrices have been performed using the method of persistent spectral hole-burning (PSHB). This technique has been used to reveal sites corresponding to distinct N-H tautomers which were not evident in the absorption spectra. An analysis of the holes and antiholes produced with PSHB in the Qx(0-0) absorption band made it possible to identify inter-conversion of distinct host sites. © 2014 AIP Publishing LLC.


PubMed | B. I. Stepanov Institute of Physics, CNRS Orsay Institute for Molecular Science, National University of Ireland, Maynooth, University Paris - Sud and Belarussian State Agrarian Technical University
Type: Journal Article | Journal: The Journal of chemical physics | Year: 2014

The absorption, fluorescence, and excitation spectra of free base tetraazaporphine (H2TAP) trapped in Ne, N2, and Ar matrices have been recorded at cryogenic temperatures. Normal Raman spectra of H2TAP were recorded in KBr discs and predicted with density functional theory (DFT) using large basis sets calculations. The vibrational frequencies observed in the Raman Spectrum exhibit reasonable agreement with those deduced from the emission spectra, as well as with frequencies predicted from large basis set DFT computations. The upper state vibrational frequencies, obtained from highly resolved, site selected excitation spectra, are consistently lower than the ground state frequencies. This contrasts with the situation in free base phthalocyanine, where the upper state shows little changes in vibrational frequencies and geometry when compared with the ground state. Investigations of the photochemical properties of H2TAP isolated in the three matrices have been performed using the method of persistent spectral hole-burning (PSHB). This technique has been used to reveal sites corresponding to distinct N-H tautomers which were not evident in the absorption spectra. An analysis of the holes and antiholes produced with PSHB in the Qx (0-0) absorption band made it possible to identify inter-conversion of distinct host sites.


Ze W.,Belarusian National Technical University | Bashkirov L.A.,Belarusian National Technical University | Trukhanov S.V.,National Academy of Sciences of Belarus | Lobanovskii L.S.,National Academy of Sciences of Belarus | And 2 more authors.
Inorganic Materials | Year: 2014

Sr1 - x Sm x Fe12 - x Co x O19 (0 ≤ x ≤ 0.5) ferrites have been prepared by solid-state reactions in air at 1470 K using mixtures of samarium oxide, ferric oxide, Co3O4, and strontium carbonate. X-ray diffraction characterization showed that the samples with x < 0.2 were single-phase, whereas the samples with 0.2 ≤ x ≤ 0.5 contained α-Fe 2O3 and those with 0.3 ≤ x ≤ 0.5 contained SmFeO3, CoFe2O4, and Sm2O 3 as well. The highest degree of Sm3+ and Co2+ substitutions for Sr2+ and Fe3+ (x) in the SrFe 12O19 ferrite at 1470 K was determined to be slightly less than 0.2. This substitution only slightly decreases the a and c parameters of the hexagonal lattice and the Curie temperature (T C) of the material. At temperatures of 5 and 300 K in magnetic fields of up to 14 T, we obtained magnetic hysteresis loops, which were used to evaluate the spontaneous magnetization (σ0), specific saturation magnetization (σs), and coercive force (σ H c) of the ferrites. The experimentally determined 5-K spontaneous magnetization per formula unit (n 0) of the x = 0.1 ferrite is 20.86μB, which coincides with the theoretical value calculated as n 0 = (8 × 5) - (3.9 × 5 - 0.1 × 3) = 20.8μB. At 300 K, the n 0 and σ H c of Sr 0.9Sm0.1Fe11.9Co0.1O19 exceed those of SrFe12O19 by 7.7 and 9.9%, respectively. © 2014 Pleiades Publishing, Ltd.


Firago V.A.,Belarussian State University | Senkov A.G.,Belarussian State Agrarian Technical University | Wojcik W.,Lublin University of Technology
Przeglad Elektrotechniczny | Year: 2010

There are analyzed opportunities of decreasing the influence of changes of hot metals' emissivity on the results of determining their thermodynamic temperature by two-and three-color pyrometers on modern 'sandwich' type and 'mosaic' type photo detectors. The dependence of the error of temperature measurement on the spectral location and spectral width of pyrometer's working spectral bands is estimated. The effectiveness of additional using of laser reflectometry together with spectral ratio method and luminous method is considered. There is suggested a three-color pyrometric method using three-color multi-element photo detectors on Si.


Troyanchuk I.O.,National Academy of Sciences of Belarus | Bushinsky M.V.,National Academy of Sciences of Belarus | Tereshko N.V.,National Academy of Sciences of Belarus | Dobryanskii V.M.,Belarussian State Agrarian Technical University | And 2 more authors.
Journal of Experimental and Theoretical Physics | Year: 2015

The magnetization and the crystal structure of the La0.7Sr0.3Mn1 − xMxO3 (M = Ga, Fe, Cr; x ≤ 0.3) systems are studied. The substitution of gallium and chromium is shown to cause phase separation into antiferromagnetic and ferromagnetic phases, whereas the substitution of iron for manganese stabilizes a spinglass state. The ferromagnetic phase in the chromium-substituted compositions is much more stable than that in the case of substitution by iron ions or diamagnetic gallium ions. The magnetic properties are explained in terms of the model of superexchange interactions and the localization of most eg electrons of manganese. The stabilization of ferromagnetism in the chromium-substituted compositions can be caused by the fact that the positive and negative contributions to the superexchange interaction between Mn3+ and Cr3+ ions are close to each other but the antiferromagnetic part of the exchange is predominant. Moreover, some chromium ions are in the tetravalent state, which maintains the optimum doping conditions. © 2015, Pleiades Publishing, Inc.


Bashkirov L.A.,Belarusian National Technical University | Slonskaya S.V.,Belarussian State Agrarian Technical University | Lubinskii N.N.,Institute for Command Engineers | Galyas A.I.,National Academy of Sciences of Belarus | And 2 more authors.
Inorganic Materials | Year: 2014

We have found that the 77-K magnetization per formula unit of the SrFeO3 - δ ferrite, Sr0.9La0.1Fe 0.9Cd0.1O3 - δ and Sr 0.75La0.75Fe0.75Cd0.75O 4 - δ mixed oxides, and SrLaFeO4 compound, calculated per mole of Fe ions, is 0.114μB, 0.024μB, 5 × 10-3 μB, and 4.3 × 10-2 μB, respectively. The resultant effective magnetic moment of the Fe3+ and Fe4+ ions (μeffFe3+,Fe4+) in the Sr0.9La0.1Fe0.9Cd0.1O 3 - δ solid solution in the temperature range 520-850 K is 3.61μB, and (μeffFe3+,Fe4+) in Sr 0.75La0.75Fe0.75Cd0.75O 4 - δ and SrLaFeO4 in the temperature ranges 350-600 and 100-550 K is 5.89μB and 5.70μB, respectively. © 2014 Pleiades Publishing, Ltd.


Karpinsky D.V.,University of Aveiro | Karpinsky D.V.,Scientific Practical Materials Research Center of Belarus | Troyanchuk I.O.,Scientific Practical Materials Research Center of Belarus | Chobot G.M.,Belarussian State Agrarian Technical University | And 3 more authors.
Physica Status Solidi (B) Basic Research | Year: 2010

Crystal structure and magnetic properties of the Pr0.5Sr0.5Co1-xFexO3-d are studied to clarify an origin of the magnetic peculiarity observed for Pr0.5Sr0.5CoO3-d compound near TA ≈ 120 K. A correlation between crystal symmetry, magnetic structure, and the magnetic anomaly is discussed. At room temperature the compounds with x < 0.67 have ortho- rhombic crystal structure described by Imma space group. Crystal symmetry of these compounds reduces down to monoclinic (triclinic) one with a temperature decrease, whereas the crystal structure of the solid solutions with x > 0.7 remains orthorhombic at low temperatures. Increase of Fe percentage changes the magnetic properties of the compounds from ferromagnetic to cluster spin-glass, spin glass and then to antiferromagnetic one. An existence of the magnetic feature is strongly dependent on the magnetic state of the compounds. The data obtained specify that a rearrangement of the bond lengths in rare-earth sublattice is responsible for the crystal structure modification and thus for the magnetic anomaly. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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