Author: norAdmin

A.D. Zigert, N.B. Kuz`min, E.M. Semenova, A.Yu. Karpenkov, A.I. Ivanova, N.Yu. Sdobnyakov
Tver State University

Abstract: The article continues a series of studies of permanent magnets with different magnetization reversal mechanisms (nucleation, domain boundary displacement). In this work, a correlation is established between magnetic characteristics of permanent magnets (Y25 and AlNiCo) and the fractal dimension of magneto-optical images of their stray fields. Bismuth-containing ferrite-garnet films were used as an indicator. It is shown that the limiting values of the fractal dimension: 1,76 for a ferrite magnet and 1,85 for an AlNiCo magnet, are consistent with the results obtained for NdFeB (grade N35) and SmCo (grade KC37) magnets, as is the behavior of the field dependence of the fractal dimension. The behavior of the field dependence of magnetization M_mo(H_rev) has similar features to a similar dependence recorded for a permanent magnet NdFeB (grade N35), but the values of the demagnetizing fields for the Y25 sample are much smaller. The paper discusses the relationship between the mechanisms of magnetization reversal of permanent magnets and the behavior of the M_mo(H_rev) dependence.
Keywords: permanent magnets, fractal dimension, magneto-optics, dM(Hrev)/dHrev dependence

V.I. Ivanov, A.V. Myagotin
Far Eastern State Transport University

Abstract: The efficiency of the recording dynamic holograms in dispersed liquid-phase media with a high concentration of nanoparticles is analyzed. The optical nonlinearity of the medium is due to the electrostriction forces acting on the particles of the dispersed phase in a gradient light field. Mass transfer is considered in the case of suprathermal radiation intensities, when the light-induced change in the concentration of nanoparticles is greater than the initial one and reaches saturation. It is shown that at high levels of the radiation intensity, the recording of a dynamic hologram is carried out in a significantly nonlinear mode, when the phase lattice becomes non-sinusoidal. At the same time, the amplitude of the first harmonic increases sharply with increasing intensity, which makes it possible to achieve a significant increase in the efficiency of the hologram recording. The results obtained are relevant for dynamic holography of dispersed liquid-phase media, as well as for optical diagnostics of such media.
Keywords: electrostriction, cubic nonlinearity, nanosuspension, dynamic holograms, suprathermal radiation intensity, optical diagnostics

V.I. Ivanov¹, I.N. Egorshin^2
1 Far Eastern State Transport University
² Pacific State University

Abstract: In this paper, a modulation method for creating a pseudo-prism in a nanodispersed liquid-phase medium is proposed, based on using the light pressure of radiation. Usually, the pseudo-prism method is used to study a stationary sedimentation profile in a dispersed medium. For nanoparticles and macroscopic cell sizes, the typical equilibrium times are tens of hours. Even with significant light pressure forces that exceed gravitational pressures, the characteristic time of settling the sedimentation profile remains very long. Therefore, achieving an equilibrium distribution requires a long experiment, which places high demands on the stability of all conditions and is practically unrealizable due to the presence of convective flows. Modulation of the reference beam makes it possible to study the dynamics of the pseudo-prism at short times, which significantly increases the accuracy of the optical diagnostic method. The article presents a theoretical analysis of the process of light-induced mass transfer in a dispersed liquid-phase medium located in a homogeneous time-modulated light field. As a result of the analytical solution of the problem of light-induced mass transfer, an expression was obtained that makes it possible to determine the amplitude of the angle of deflection of the signal beam in a pseudo-prism.
Keywords: pseudoprism method, light pressure, nanofluids, optical diagnostics, separation, nanoparticles

Yu.F. Ivanov¹, Yu.Kh. Akhmadeev¹, A.A. Klopotov², N.A. Prokopenko¹, E.A. Petrikova¹, O.V. Krysina¹, V.V. Shugurov¹, A.N. Shmakov³, V.Yu. Lavrov^2
1 Institute of High- Current Electronics of the Siberian Branch of the RAS
² Tomsk State University of Architecture and Building
³ Boreskov Institute of Catalysis of the Siberian Branch of the RAS

Abstract: High-entropy alloys based on refractory metals, possessing an unusual combination of physical, mechanical, tribological, electrophysical, etc. properties, can be recommended for use in various fields of industry and medicine. The aim of the work is to study the growth process of high-entropy alloys films of the Ti-Nb-Zr-Ta-Hf-Cu system in real time by X-ray phase analysis using synchrotron radiation. Experiments on the deposition of multielement metal films were carried out on the VEIPS-1 setup developed at the Institute of high current electronics Siberian branch of the Russian academy of sciences for studying the processes of the film and coating formation on a synchrotron radiation source. The process of in situ thin film structure formation with high time resolution was studied using a synchrotron radiation source – the VEPP-3 electron storage ring, the Institute of nuclear physics, Siberian branch of the Russian academy of sciences. It is shown that the deposition of Ti-Nb-Zr-Ta-Hf-Cu plasma on a HG40 substrate is accompanied by the formation of an amorphous-crystalline state represented by phases of the composition (presumably) Ti-Nb-Zr-Ta-Hf-Cu, TiZr, NbZr, and CuTiZr, formed at different stages of film deposition. The main phase is the Ti-Nb-Zr-Ta-Hf-Cu composition.
Keywords: high-entropy alloy, refractory metals, synchrotron radiation, phase composition, copper alloying

A.I. Ivanova, A.V. Dudilovskaya, O.E. Zhuravlev, A.D. Kaphtanov
Tver State University

Abstract: This article presents the results of studying non-conducting biological, crystalline objects, powders, and glass composite samples using an ionic liquid by scanning electron microscopy. Ionic liquids based on alkylpyridinium dicyanamides studied in the work were obtained by a metathesis reaction. A solution of ionic liquid in acetone was used as a conductive coating for dielectrics. It was found that the use of ionic liquid is an alternative to the methods of metal and carbon sputtering on dielectric samples. Scanning electron microscopy images of samples obtained by such microscopy methods as low vacuum mode, the use of metal sputtering (Pt) on samples, and a study of samples without a conductive coating are presented. A comparative analysis of the results obtained by traditional methods and the method of applying ionic liquid to samples is carried out. It is shown that the use of electrically conductive ionic liquids with the thermal and chemical stability makes it possible to obtain high-resolution electron microscopic images and also allows visualization of the topographic and compositional contrast of the studied dielectric samples.
Keywords: ionic liquid, sample preparation, dielectric samples, surface microstructure, scanning electron microscopy

Yu.V. Kabirov¹, A.A. Utoplov¹, N.V. Lyanguzov¹, E.N. Sidorenko¹, N.V. Prutsakova², E.V. Chebanova^2
1 Southern Federal University
² Don State Technical University

Abstract: The paper studies the dependence of the magnetoresistance and Seebeck coefficient of the composite magnetoresistive composition near the percolation threshold of 80%La_0,7Sr_0,3MnO₃/20%GeO₂ on the constant magnetic field strength up to 3,8 kOe and temperature in the range from 25°C to 150°C. The 80%La_0,7Sr_0,3MnO₃/20%GeO₂ samples have the p-type conductivity, a the positive sign of the Seebeck coefficient and a dielectric character of the change in the electrical resistance with temperature. The activation energy of such compositions is of about 0,35 eV. The magnetoresistance of such a composition decreases with an increase in the temperature difference between the hot and cold edges and disappears in the region of the phase transition temperatures of 90°C. It was found that in a constant external magnetic field of 3,8 kOe, a decrease in the Seebeck coefficient of the 80%La_0,7Sr_0,3MnO₃/20%GeO₂ compositions by 11% is observed at a temperature difference of 10 K. The dependence of the Seebeck coefficient on the magnetic field decreases with an increase in the hot edge temperature and also disappears in the temperature range of 90°C, which is associated with the ferromagnetic-paramagnetic phase transition of lanthanum manganite La_0,7Sr_0,3MnO₃ and the suppression of spin-dependent electron tunneling.
Keywords: Seebeck coefficient, magnetoresistive composite, constant magnetic field, lanthanum- strontium manganite, percolation

I.L. Kislova¹, D.A. Kiselev², A.L. Kholkin^3,4, A.V. Solnyshkin¹, O.A. Muhin¹, G.G. Kolkov^1
1 Tver State University
² National University of Science and Technology MISIS
³ Aveiro Institute of Materials
⁴ Institute of Solid-State Physics, University of Latvia

Abstract: In this work, the polarization distribution over the volume of (1-x)Pb(Zn_1/3Nb_2/3)O_3-xPbTiO₃ crystals of the directions [001] and [111] was studied by the method of dynamic pyroelectric response. It is established that the value of the pyroelectric coefficient in the samples of both directions is the same. The domain structure of the studied crystals was visualized by piezoresponse force microscopy. It is shown that on the surface of the initial single crystals of these directions there is a small-sized labyrinth-like domain structure from 50 to 500 nm, characteristic of ferroelectric relaxors. At a depth of 50 microns from the crystal surface, a larger domain structure with a characteristic micron-scale domain size is observed. To determine the average thickness of a layer with an inhomogeneous polarization distribution, a theoretical model was used that analytically describes the possibilities of a dynamic pyroelectric method for studying the near-surface layer of ferroelectric materials. Theoretical calculations have shown that this method allows us to obtain accurate data on the thickness of the layer and its polarization state. It has been experimentally established that in a single crystal 0,955Pb(Zn_1/3Nb_2/3)O_3-0,045PbTiO₃ of the direction [001], the secondary pyroelectric effect contributes to the overall pyroelectric response much more than for the direction [111] due to the large value of the piezoelectric coefficient.
Keywords: relaxors, pyroelectric effect, polarization, piezoelectric force microscopy, domain structure

N.S. Kozhevnikova^1,2, E.A. Bogdanova^1,3, V.M. Skachkov¹, I.V. Baklanova¹, A.P. Tyutyunnik¹, L.Yu. Buldakova¹, M.Yu. Yanchenko¹, A.A. Yushkov^2
1 Institute of Solid State Chemistry of the Ural Branch of RAS
² Ural Federal University named after the first President of Russia B. N. Yeltsin
³ JSC «Giredmet»

Abstract: The article discusses the possibility of obtaining functional composite materials with pronounced photocatalytic properties. A hybrid composite material based on nanoscale cadmium sulfide fixed on a matrix of hydroxyapatite obtained by precipitation from solution has been developed. The initial components and synthesized samples were certified using some modern physico-chemical analysis methods: X-ray phase analysis, energy dispersive X-ray analysis, Raman spectroscopy, scanning electron microscopy, the Brunauer-Emmett-Teller method. The functional characteristics of the developed composite material Ca₁₀(PO₄)₆(OH)_2-CdS, in particular, the photocatalytic activity under the action of ultraviolet or visible radiation, are investigated. The efficiency of using the developed composite material as a photocatalyst was evaluated by the rate of oxidation of p-dihydroxybenzene (hydroquinone). Based on experimental data obtained, the values of the constants of the reaction rate of photocatalytic oxidation of hydroquinone and the time of its half-conversion under various conditions (radiation, the presence of a catalyst) are calculated. It is proved that the developed composite material, which is a hydroxyapatite modified with colloidal CdS particles, has pronounced catalytic properties and is a promising material for use as a photocatalyst. A patent application has been filed for the developed composite material.
Keywords: cadmium sulfide, chemical condensation from aqueous solutions, hydroxyapatite, composite material, photocatalysis

D.A. Kravchenko, A.Yu. Kolosov, D.N. Sokolov, N.I. Nepsha, S.S. Bogdanov, N.Yu. Sdobnyakov
Tver State University

Abstract: A comparative study combining the experimental technique of scanning electron microscopy and atomistic simulation by (molecular dynamics) was carried out using of the ternary CoCrMo nanoalloy as an example. Employing the technology of selective laser melting based on the PR-KH28M6 powder, a sample was made for which a non-uniform surface composition with respect to the presence of cobalt and chromium was identified, i.e. areas were simultaneously enriched and depleted in these elements, which indicates the possibility of forming various intermetallic compounds based on them. In the process of atomistic simulation, three nanoparticles of the ternary CoCrMo nanoalloy with the number of 10000, 15000 and 30000 atoms were subjected to a sequential cycle of heating and cooling, including the identification of phase transitions corresponding to melting and crystallization, respectively. The corresponding temperatures of the beginning and end of the phase transition were determined. The regularities of structural and surface segregation in the ternary CoCrMo nanoalloy are described. It is noted that for nanoparticles containing 10000 atoms, only a shell of cobalt atoms is formed without forming a core, while for nanoparticles containing 15000 and 30,000 atoms, an onion-like structure is formed. Chromium atoms form either the core of the nanoparticle as at N=10000 or the peripheral region as at N=15000 and 30000. Molybdenum atoms behave indifferently, i.e. are distributed uniformly throughout the entire volume of the nanoparticles under study.
Keywords: ternary CoCrMo alloy, selective laser melting technology, surface microstructure, molecular dynamics method, structural and surface segregation

M.N. Lapushkin
Ioffe Institute

Abstract: For the first time, the adsorption of barium atoms on the surface of the (0001) face of GaN was calculated using the density functional method. The 2D GaN layer was modeled using a GaN(0001) 2×2 supercell containing 10 GaN bilayers. The electron density of state and the adsorption energy of the Ba atom were calculated for five adsorption sites of the Ba atom: in the hollow position, in the bridge position between the surface Ga (N) atoms, and above the surface Ga (N) atom. There was one Ba atom per 4 surface Ga atoms in the first GaN bilayer. The adsorption of the barium atom above the surface N atom was most preferable. The adsorption energy was 2,96 eV. The adsorption of Ba atoms resulted in an insignificant reconstruction of the GaN surface: the maximum shift of the Ga (N) atoms did not exceed 0,11 Å. The adsorption of Ba resulted in the formation of a surface band below the Fermi level.
Keywords: density functional method, electronic structure, interface, surface, adsorption, barium, GaN