Papers by Author: Oleg Stognei

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Authors: Anton Grebennikov, Oleg Stognei
Abstract: Magnetoresistive effect and electrotransport properties of Niх(MgO)100-х (x: 21-48 at.%) granular composites have been investigated. It is found that prepercolated composites (x < 24 at.%) do not exhibit magnetoresistive properties. After percolation threshold (x: 27-29 at.%) the composites exhibit isotropic negative magnetoresistance (-0,2 %) which has not tunneling nature. Also weak localization is realized in these samples at temperatures below 100 K. At high metal concentration (32 at.% < x) the composites exhibit anisotropic magnetoresistance.
Authors: Anton Grebennikov, Oleg Stognei, Konstantin Semenenko, Tatijana Tregubova
Abstract: Magnetoresistive effect and electrotransport properties of Fe-NbO (13 ≤ Fe, at.% ≤ 80) thin films annealed at 600 °C has been investigated. It has been established that the samples structure contains three main phases Fe, NbO2, Fe2.9O4. Maximum of magnetoresistance in the samples does not exceed 0.3%, a coercive force is ranging from 150 to 370 Oe, depending on the Fe concentration. It is assumed that the films have a granular structure. Magnetoresistance and coercive force values, as well as the correlation between the magnetoresistance and the magnetization of the Fe-NbO samples are uncharacteristic for granular systems. It is assumed that uncharacteristic properties are due to the significant influence of ferrite Fe2.9O4 on the magnetic properties and electrotransport of the Fe-NbO films.
Authors: Oleg Stognei, Ahmed Al-Maliki, Alexander Sitnikov, Vladimir Makagonov
Abstract: Nanocomposite Fex(Al2O3)100-x films with concentration gradient along the long axis of the samples (40 mm) have been obtained by sputter deposition technique and investigated. Based on the electric and magnetoresistive investigations the gradient Fex(Al2O3)100-x samples in which concentration of one edge of the sample is smaller than concentration of a percolation threshold while concentration of opposite edge of this sample is upper the threshold have been determined. Influence of the heat flow direction on the thermoelectric power of the gradient samples has been investigated. Hysteresis of the thermoelectric power is observed when temperature gradient direction is changed.
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