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1
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Spin-Polarized and Normal Hopping Magnetoresistance in Heavily Doped Silicon

100%
Fedotov A., Prischepa S., Danilyuk A., Svito I., Zukowski P.
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vol. 125
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issue 6
1271-1275
EN
Investigation of electrical resistivity ρ and magnetoresistance in single crystalline n-type silicon heavily doped with antimony in the temperature range ΔT=5-300 K and at the magnetic inductance B up to 8 T was performed. It was established that, for the temperature range ΔT=25-300 K the conductivity is of activation type, while for ΔT=5-25 K it is of variable range hopping and is described by the Mott law. Parameters of the Mott hopping were calculated. It was shown that, to explain the experimental data, the spin polarized hopping via the occupied states has to be taken into account. The obtained parameters revealed that for the low temperature range ΔT=5-11 K the spin polarized hopping dominates, while for ΔT=11-20 K the spin polarized transport is accompanied by the wave function contraction.
2
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Percolation Phenomena in Cu_{x}(SiO_{y})_{100-x} Nanocomposite Films Produced by Ion Beam-Sputtering

100%
Koltunowicz T., Zukowski P., Czarnacka K., Svito I., Fedotov A.
Acta Physica Polonica A
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2015
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vol. 128
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issue 5
908-911
EN
In this paper the results of examinations of nanocomposites Cu_{x}(SiO_{y})_{100-x} produced by ion beam sputtering using argon ions were presented. The examinations were performed by the use of ac devices for measuring frequency in the range 50 Hz-1 MHz and temperatures from 81 K to 273 K. The measurements were performed for the samples directly after production. Based on temperature dependences of conductivity σ , which were determined at the frequency 100 Hz, the Arrhenius graphs were prepared. From these graphs conductivity activation energies ΔE were calculated. Dependences of conductivity and activation energy of electrons on the metallic phase content x at the frequency 100 Hz were determined. Analysis of the obtained dependences shows that conductivity is a parabolic function of the metallic phase content x in nanocomposites. Changes of activation energies of nanocomposites, in which metallic phase contents are in the ranges x < 12 at.% and x > 68 at.%, demonstrate negative values - metallic type of conductivity. In the range 12 at.% < x < 68 at.% activation energies have positive values - the dielectric type of conductivity. It was established that for the metallic phase content of about 68 at.% the real percolation threshold occurs, and the conduction changes from dielectric to metallic type.
3
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Low-Temperature DC Carrier Transport in (Co_{0.45}Fe_{0.45}Zr_{0.10})_{x}(Al_2O_3)_{1-x} Nanocomposites Sputtered in Mixed Argon-Oxygen Atmosphere

86%
Svito I., Fedotov A., Saad A., Koltunowicz T., Zukowski P., Bury P.
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vol. 125
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issue 6
1351-1355
EN
This paper studies the temperature dependences (2 < T < 300 K) of the DC conductivity σ(T) for the (Co_{0.45}Fe_{0.45}Zr_{0.10})_x(Al_2O_3)_{1-x} nanocomposites (30 < x < 65 at.%) sputtered in Ar + O_2 atmosphere. It is shown that at temperatures lower than 100-150 K dependences of DC conductance on temperature for all the studied samples are due to the Shklovski-Efros variable range hopping mechanism. It was also observed that σ(x,T) dependences can be attributed to the formation of FeCo-based oxide "shells" around metallic alloy nanoparticles due to incorporation of oxygen in the vacuum chamber during the deposition procedure.
4
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Mechanisms of Carrier Transport in Cu_x(SiO₂)_{1-x} Nanocomposites Manufactured by Ion-Beam Sputtering with Ar Ions

86%
Fedotov A., Mazanik A., Svito I., Saad A., Fedotova V., Czarnacka K., Koltunowicz T.
Acta Physica Polonica A
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2015
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vol. 128
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issue 5
883-886
EN
The present paper investigates the temperature/frequency dependences of admittance Z in the granular Cu_x(SiO₂)_{1-x} nanocomposite films around the percolation threshold x_{C} in the temperature range of 4-300 K and frequencies of 20-10⁶ Hz. The behavior of low-frequency ReZ(T) dependences displayed the predominance of electrons hopping between the closest Cu-based nanoparticles for the samples below the percolation threshold x_{C} ≈ 0.59 and nearly metallic behaviour beyond the x_{C}. The high-frequency curves ReZ(f) at temperatures T > 10 K for the samples with x < x_{C} exhibited behavior close to ReZ(f) ≈ f^{-s} with s ≈ 1.0 which is very similar to the known Mott law for electron hopping mechanism. For the samples beyond the percolation threshold (x > x_{C}), the frequency dependences of ReZ(f) displayed inductive-like (not capacitive) behaviour with positive values of the phase shift angles.
5
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Voltage and Current Resonance in Nanocomposite (FeCoZr)_x(CaF₂)_{100-x} Produced by Ion-Beam Sputtering in Pure Argon Atmosphere

86%
Koltunowicz T., Zukowski P., Bondariev V., Fedotov A., Svito I., Fedotova J., Saad A.
Acta Physica Polonica A
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2015
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vol. 128
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issue 5
897-900
EN
In this paper the results of investigations of electrical properties of metal-dielectric nanocomposites (FeCoZr)_x(CaF₂)_{100-x} are presented. The samples with the metallic phase content x=45.7 at.% were produced by ion-beam sputtering method in pure argon atmosphere, and subsequently annealed at 398 K for 15 min. The measurements of electrical properties were performed in the frequency range from 50 Hz to 1 MHz. The frequency dependences of phase angle θ, capacity C_{p}, conductivity σ and dielectric loss factor tanδ were measured at seven different temperatures ranging from 148 K to 263 K. It was found that the nanocomposite exhibits the phenomena of voltage resonance and current resonance, characteristic of the conventional RLC circuits with series and parallel connections of elements.
6
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Thermoelectric Properties of Ca_3Co_4O_9-Based Ceramics Doped with Fe and/or Y

73%
Fedotov A., Fedotov A., Mazanik A., Svito I., Saad A., Troyanchuk I., Bushinski M., Fedotova V., Zukowski P., Koltunowicz T.
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vol. 125
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issue 6
1344-1347
EN
We describe here structure and temperature dependences of conductivity σ(T), the Seebeck coefficient α(T), thermal conductivity λ(T) and figure-of-merit ZT(T) in Ca_3Co_4O_9 ceramics, doped with Fe and Y, depending on compacting pressure (0.2 or 6 MPa) and temperature (300 < T < 700 K). It is shown that introduction of iron and yttrium to ceramics does not alter the crystalline structure of the material. Increasing the pressure in the compacting process before the additional diffusion annealing leads to a smaller-grained structure and increase σ and λ due to reducing of the synthesized samples porosity. The Seebeck coefficients of nanocomposite ceramics Ca_3Co_{3.9}Fe_{0.1}O_9 and (Ca_{2.9}Y_{0.1})(Co_{3.9}Fe_{0.1})O_9 have linear dependences on temperature is not changed after increase of compacting pressure. Electrical-to-heat conductivity ratio (σ/λ) for the samples compacted at high (6 GPa) pressure increases not more than 20-30% in comparison with ones compacted at low (0.2 GPa) pressure, whereby ZT is increased more than 50%. The main reason for this effect is samples porosity reduction with the compacting pressure increase.
7
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Magnetotransport in Si ⟨Sb⟩ Delta-Layer after Swift Heavy Ion-Induced Modification

73%
Fedotov A., Skuratov V., Yurasov D., Novikov A., Svito I., Apel P., Fedotov A., Zukowski P., Fedotova V.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
229-232
EN
In the present paper the investigations of the influence of swift heavy ion irradiation on the magnetotransport in the antimony (Sb) δ-layer in silicon are reported. Temperature and magnetic field dependences of the resistance R(T,B) and the Hall coefficient R_H(T,B) in the temperature range of 2K < T < 300K and B ≤ 8T before and after the 167 MeV Xe⁺²⁶ ion irradiation (ion fluence of 10⁸ cm¯²) were measured. At the temperatures below 50K there is observed the transition from the Arrhenius log R(1/T) to a logarithmic R ≈ -log(T) dependence both before and after the swift heavy ion exposure which confirms the assumption that the carrier transport goes through the δ-layer mainly. Moreover, the transition from the positive to negative magnetoresistance was observed with the temperature decrease that is characteristic of the two-dimensional quantum corrections to the conductivity in the case of weak localization regime. The appropriate Thouless lengths L_{Th}(T) ≈ A × T^{p} (where p and A are dependent on the scattering mechanism) indicated their ≈ 25-30% decrease after the swift heavy ion exposure. It was shown that the exponent p values were close to the theoretical one of p = 1, confirming the realization of 2D weak localization regime in the carrier transport.
8
Content available remote

Ion Irradiation of Oxidized FeCoZr-CaF₂ Nanocomposite Films for Perpendicular Magnetic Anisotropy Enhancement

73%
Kasiuk J., Fedotova J., Przewoźnik J., Kapusta C., Skuratov V., Svito I., Bondariev V., Kołtunowicz T.
Acta Physica Polonica A
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2017
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vol. 132
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issue 2
206-209
EN
The paper is focused on the results of Xe ions irradiation of nanocomposite FeCoZr-CaF₂ films synthesized in the oxygen-containing atmosphere. Combined influence of nanoparticles partial oxidation and ion irradiation with different fluences on the crystalline structure, phase composition and magnetic anisotropy is analysed by X-ray diffraction, the Mössbauer spectroscopy and vibrating sample magnetometry. The origin of the detected progressive enhancement of perpendicular magnetic anisotropy as the result of films oxidation and irradiation is discussed in the context of formation of nanoparticles oxide shells and ion tracks along the films normal.
9
Content available remote

Anisotropic Magnetoresistance of Ni Nanorod Arrays in Porous SiO₂/Si Templates Manufactured by Swift Heavy Ion-Induced Modification

73%
Fedotova J., Ivanou D., Mazanik A., Svito I., Streltsov E., Saad A., Zukowski P., Fedotov A., Bury P., Apel P.
Acta Physica Polonica A
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2015
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vol. 128
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issue 5
894-896
EN
In this work anisotropic magnetoresistance in nanogranular Ni films and Ni nanorods on Si(100) wafer substrates was studied in wide ranges of temperature and magnetic field. To produce Ni films and nanorods we used electrochemical deposition of Ni clusters either directly on the Si substrate or into pores in SiO₂ layer on the Si substrate. To produce mesopores in SiO₂ layer, SiO₂/Si template was irradiated by a scanned beam of swift heavy 350 MeV ¹⁹⁷Au²⁶⁺ ions with a fluence of 5×10⁸ cm¯² and then chemically etched in diluted hydrofluoric acid. Pores, randomly distributed in the template have diameters of 100-250 nm and heights about 400-500 nm. Comparison of temperature dependences of resistance and magnetoresistance in Ni films and n-Si/SiO₂/Ni structures with Ni nanorods showed that they are strongly dependent on orientation of magnetic field and current vectors relative to each other and the plane of Si substrate. Moreover, magnetoresistance values in n-Si/SiO₂/Ni nanostructures can be controlled not only by electric field applied along Si substrate but also by additionally applied transversal bias voltage.
10
Content available remote

Magnetoresistance in n-Si/SiO_2/Ni Nanostructures Manufactured by Swift Heavy Ion-Induced Modification Technology

59%
Fedotova J., Ivanou D., Ivanova Y., Fedotov A., Mazanik A., Svito I., Streltsov E., Saad A., Tyutyunnikov S., Kołtunowicz T., Demyanov S., Fedotova V.
Acta Physica Polonica A
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2011
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vol. 120
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issue 1
133-135
EN
A study of magnetotransport in the n-Si/SiO_2/Ni nanostructures with granular Ni nanorods in SiO_2 pores was performed over the temperature range 2-300 K and at the magnetic fields induction up to 8 T. The n-Si/SiO_2/Ni Schottky nanostructures display the enhanced magnetoresistive effect at 25 K due to the impurity avalanche mechanism.
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