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Belogolovskii M.,Donetsk Institute for Physics and Engineering | Lacquaniti V.,National Institute of Metrological Research
Springer Proceedings in Physics | Year: 2014

Theoretical and experimental analysis of electron transport across ultrathin, homogeneously disordered oxide layers is presented with particular regard to the question of how much the effects are universal. We show that (i) distribution of transparencies across dirty subnanometer-thick insulating films is bimodal and (ii) conductance-voltage characteristics of oxide layers with thicknesses increased up to several nanometers are power functions with an index near 1.3. The universality of transport properties is explained as an effect of strong local barrier-height fluctuations generated by the presence of oxygen vacancies. © Springer International Publishing Switzerland 2014.

Krasnyuk I.B.,Donetsk Institute for Physics and Engineering | Taranets R.M.,Ukrainian Academy of Sciences | Chugunova M.,Claremont Graduate University
Physica A: Statistical Mechanics and its Applications | Year: 2014

This paper examines surface-induced ordering in confined binary alloys. The hyperbolic initial boundary value problem (IBVP) is used to describe a scenario of spatiotemporal ordering in a disordered phase for concentration of one component of binary alloy and order parameter with non-linear dynamic boundary conditions. This hyperbolic model consists of two coupled second order differential equations for order parameter and concentration. It also takes into account effects of the "memory" on the ordering of atoms and their densities in the alloy. The boundary conditions characterize surface velocities of order parameter and concentration changing which is due to surface (super)cooling on walls confining the binary alloy. It is shown that for large times there are three classes of dynamic non-linear boundary conditions which lead to three different types of attractor's elements for the IBVP. Namely, the elements of attractor are the limit periodic simple shock waves with fronts of "discontinuities" Γ. If Γ is finite, then the attractor contains spatiotemporal functions of relaxation type. If Γ is infinite and countable then we observe the functions of pre-turbulent type. If Γ is infinite and uncountable then we obtain the functions of turbulent type. © 2014 Published by Elsevier Ltd.

Mitsiuk V.I.,National Academy of Sciences of Belarus | Tkachenka T.M.,National Academy of Sciences of Belarus | Budzynski M.,Maria Curie Sklodowska University | Surowiec Z.,Maria Curie Sklodowska University | Valkov V.I.,Donetsk Institute for Physics and Engineering
Nukleonika | Year: 2013

Magnetic and Mössbauer measurements were performed for Mn2-xFexP0.5As0.5, 0.5 ≤ x ≤ 1.0. It was shown that with decreasing Fe content magnetic interaction significantly weakens. Low temperature magnetic structure could be explained as a superposition of ferromagnetic and antiferromagnetic contributions to the whole magnetic moment of the alloy.

Tikhii A.,Taras Shevchenko National University | Gritskih V.,Taras Shevchenko National University | Kara-Murza S.,Taras Shevchenko National University | Korchikova N.,Taras Shevchenko National University | And 3 more authors.
Physica Status Solidi (C) Current Topics in Solid State Physics | Year: 2013

We report on the influence of temperature conditions of deposition and annealing given on the optical conductivity spectra of LSMO films. The investigated films were deposited using DC magnetron sputtering of La0.7Sr0.3MnO3 target in argon-oxygen atmosphere on hot (T = 970 K), and cold (T=300 K) single crystalline substrates of Al2O3 (012). All films were obtained using these technologies are oxygen deficient. Optical transmission was measured in a range 1-5 eV. The optical conductivity spectra of films with thickness more than 100 nm deposited on hot substrates are slightly dependent on the annealing. These spectra are similar to the corresponding ones of epitaxial films La0.7Sr0.3MnO3 but the typical spectral peaks are slightly shifted to higher energies. The optical conductivity spectra of unannealed films with the thickness less 100 nm which are deposited on the cold and hot substrates do not have the corresponding peak near 1 eV. We explain this fact by means of size effects and oxygen deficit. These factors suppress the mechanism of eg-eg transition between Mn3+-Mn4+ ions within parallel spin manifold. The three-hour annealing in the air on the temperature interval 1070-1170 K eliminates the oxygen deficiency in films. As a result all optical properties of all investigated films are unified. Besides, the conductivity spectra of the annealed films are similar to the corresponding ones of La0.7Sr0.3MnO3 epitaxial films. But some shift of the low-energy peak to higher energies can be observed. It may correspond to polycrystallinity of obtained structures. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lyashenko I.A.,Sumy State University | Metlov L.S.,Donetsk Institute for Physics and Engineering | Khomenko A.V.,Sumy State University | Chepulskyi S.N.,Sumy State University
Journal of Nano- and Electronic Physics | Year: 2011

A non-equilibrium thermodynamic model describing the behavior of an ultrathin lubricating material film confined between two atomically-smooth solid surfaces is proposed. As the order parameter the excess volume is chosen whose value increases with melting and subsequent fluidization of lubricant. It is shown that the external pressure, applied perpendicularly to the friction surfaces, influences crucially the lubricant behavior. The total system of kinetic equations is written down in which the relative shear velocity of rubbing surfaces, their temperature, and external normal pressure are the control parameters. Phase diagram with domains of different friction regimes is built. © 2011 SumDU.

Solin N.I.,RAS Institute of Metal Physics | Korolyov A.V.,RAS Institute of Metal Physics | Medvedev Y.V.,Donetsk Institute for Physics and Engineering | Nikolaenko Y.M.,Donetsk Institute for Physics and Engineering | And 3 more authors.
Journal of Magnetism and Magnetic Materials | Year: 2013

This work is devoted to study the influence of the Griffiths phase in colossal magnetoresistance manganites. Griffiths-phase-like behavior of the paramagnetic susceptibility χ0 is observed in Nd 0.5Sr0.5MnO3 oxygen-deficient thin films fabricated by magnetron sputtering deposition. In Nd0.5Sr 0.5MnO3-δ films with oxygen deficiency for T G≈260-280 K>T>TC=138 K (TG and T C - Griffiths and Curie temperatures, respectively), paramagnetic matrix consists of a magnetic phase with short-range order (∼1-1.5 nm) (which is responsible for the colossal magnetoresistance (CMR) above T C), and is embedded in this matrix region with long-range ferromagnetic order (≫10 nm), responsible for the Griffiths phase-like behavior of the paramagnetic susceptibility. Electrical resistivity is caused by carrier tunneling between the localized states and obeys the Efros-Shklovskii law. Magnetic resistivity is caused by change of the localized state sizes under the magnetic field. The temperature and magnetic field dependencies of size of the phase inhomogeneity inclusions, found from measurements of magneto-transport properties, can be satisfactorily described by the model of thermodynamic phase separation into metallic droplets of small radius in a paramagnetic matrix. Intrinsic nanoscale inhomogeneities caused by thermodynamic phase separation, rather than the Griffiths phase, determine the electrical resistivity and colossal magnetoresistance of the films. In half-doped manganites, the nature of long-range ordered magnetic phases may be related, besides the chemical heterogeneity, to proximity to a ferromagnetic-antiferromagnetic boundary at the phase diagram as well. The results are in good agreement with the model of existence of an analog of Griffiths phase temperature in half-doped manganites. © 2013 Elsevier B.V.

Gorb E.V.,University of Kiel | Filippov A.E.,University of Kiel | Filippov A.E.,Donetsk Institute for Physics and Engineering | Gorb S.N.,University of Kiel
Arthropod-Plant Interactions | Year: 2013

Myrmecochory or seed dispersal by ants is a widely spread phenomenon, and myrmecochorous plants constitute a large portion of species in many ecosystems. Since the ant species complex in the ecosystem is continuously changing in time and space, the long-term effects of such ant-plant interactions on the plant community remained unclear. The manifold information obtained in numerous previous studies from one ecosystem in the deciduous forests of Central Ukraine allowed us to simulate the possible scenarios for plant survival and distribution in the ecosystem after a reduction in the number or local extinction of one of the ant species. The results of the virtual long-term experiment show that the abundance and spatial distribution of myrmecochorous plants strongly depends on both the abundance of ants and their species composition in the ecosystem. The positive role of ant species diversity for maintaining myrmecochorous plant species diversity is shown. Competition between plant species for seed dispersers is influenced by the ant community in such a way that the disappearance of one ant species may lead to the reduction or even local extinction of a particular plant population. © 2012 Springer Science+Business Media Dordrecht.

Novokhatska A.,Donetsk Institute for Physics and Engineering | Akimov G.,Donetsk Institute for Physics and Engineering | Prylypko S.,Donetsk Institute for Physics and Engineering | Revenko Y.,Donetsk Institute for Physics and Engineering | Burkhovetsky V.,Donetsk Institute for Physics and Engineering
Journal of Applied Physics | Year: 2013

An effect of microstructure on magnetoresistive properties of manganite ceramics (La0.65Sr0.35)0.8Mn 1.2O3±Δ with superstoichiometric manganese has been studied after sintering in the temperature range of 800-1500°C. Increase in sintering temperature to 1400°C, an enormous growth of grains, densification of material, and rise in magnetoresistance peak from 1% to 4.8% are observed. At the same time, sintering at 1500°C leads to a sharp increase in the grain size more than 100 μm, release of excess manganese on grain boundaries, and almost two times magnetoresistance peak rise. We propose that such radical changes are due to the presence of superstoichiometric manganese which plays a crucial role in the formation of ceramics microstructure and properties. © 2013 AIP Publishing LLC.

Konstantinova T.,Donetsk Institute for Physics and Engineering | Glazunova V.,Donetsk Institute for Physics and Engineering
High Pressure Research | Year: 2012

The structure of metal alloys, deformed under high pressure, has been investigated. The structural changes, leading to the formation of fragments with large-angle boundaries, are revealed by transmission electron microscopy (TEM) and high-resolution electron microscopy (HRTEM) of a typical Ti-Nb alloy. The direct observation of local crystal lattice bend supports previously developed views on dipole local bending formation (displanation) as on independent deformation mechanism, leading, first, to the structural transformation from dipole dislocation charges to local crystal lattice dipole bending zones, then, from bending zones to disclination boundaries and to further grain refinement. High pressure treatment favors the creation of dipole dislocation charges and the consequent formation of local lattice bending zones. © 2012 Taylor & Francis.

Kononenko V.V.,Donetsk Institute for Physics and Engineering | Tarenkov V.Y.,Donetsk Institute for Physics and Engineering | Dyachenko A.I.,Donetsk Institute for Physics and Engineering | Varyukhin V.N.,Donetsk Institute for Physics and Engineering
Solid State Phenomena | Year: 2014

We investigated transport characteristics of composite that consist of the superconductor MgB2 and ferromagnetic half-metallic nanoparticles La0.7Ca0.3MnO3 (LCMO). The experiments were carried out in a wide temperature range with different volume content of the magnetic impurity. It was found that over 25% of the impurity manganite breaches percolation paths of the diboride magnesium. This leads to a considerable broadening of the MgB2 superconducting transition and the formation of the network of contacts through the ferromagnetic inclusions. This result shows the possibility of the spin - activated surface realization on the superconductor - manganite boundary. It's allowing the free transition of Cooper pairs with s - wave symmetry of the order parameter in a ferromagnet with 100% spin-polarized carriers. © (2014) Trans Tech Publications, Switzerland.

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