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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

100%
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.
2
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Mechanisms of Carrier Transport in Cu_x(SiO₂)_{1-x} Nanocomposites Manufactured by Ion-Beam Sputtering with Ar Ions

88%
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.
3
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Percolation Phenomena in Cu_{x}(SiO_{y})_{100-x} Nanocomposite Films Produced by Ion Beam-Sputtering

88%
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.
4
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Charge Carrier Dynamics in Ga_{1-x}Mn_{x}As Studied by Resistance Noise Spectroscopy

75%
Lonsky M., Teschabai-Oglu J., Pierz K., Sievers S., Schumacher H., Yuan Y., Böttger R., Zhou S., Müller J.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
520-522
EN
We report on electronic transport measurements of the magnetic semiconductor Ga_{1-x}Mn_{x}As, whereby the defect landscape in various metallic thin films (x=6%) was tuned by He-ion irradiation. Changes in the distribution of activation energies, which strongly determine the low-frequency 1/f-type resistance noise characteristics, were observed after irradiation and can be explained by deep-level traps residing in the As sublattice. Various other kinds of crystalline defects such as, for instance, Mn interstitials, which possibly form nanoscale magnetic clusters with a fluctuating spin orientation, also contribute to the 1/f noise and can give rise to random telegraph signals, which were observed in films with x=7%. In addition, we neither find evidence for a magnetic polaron percolation nor any features in the noise near the Curie temperature.
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