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1
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Application of Pair Approximation to Bound-Magnetic-Polaron State in Diluted Magnetic Semiconductors

100%
Bednarski H., Spałek J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1052-1055
EN
We present a fully quantum-mechanical model of the bound magnetic polaron state in a diluted magnetic semiconductor based on the pair approximation to the exchange interaction among localized magnetic moments (spins). The model is applicable also to the limiting situation of the bound magnetic polaron magnetization due to the spins approaching saturation. On its basis, a simple extension of the Dietl-Spałek bound magnetic polaron theory is proposed and compared with the data for p-Cd_{0.95}Mn_{0.05}Te.
2
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On Concentration Dependence of Spin-Glass Freezing Temperature in Mn-Alloyed II-V Compounds

100%
Bednarski H., Cisowski J.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
868-870
EN
Basing on recent studies of the magnetic properties of (Zn_{1-x}Mn_{x})_{3}As_{2} (ZMA) and (Cd_{1-x}Mn_{x})_{3}As_{2} (CMA) as well as on theoretical works devoted to the Mn-Mn interaction in semimagnetic semiconductors, we have determined the distance dependence of this interaction taking into account the complicated crystal structure of both systems. The resulting radial dependence of the exchange interaction (being a sum of superexchange and the Bloembergen-Rowland mechanism) together with the scaling analysis have allowed us to describe the Mn-concentration dependence of spin-glass freezing temperature in ZMA, CMA and, for comparison, also in Cd_{1-x}Mn_{x}Te in very good agreement with experimental data.
3
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Bound-Magnetic-Polaron Molecule in Diluted Magnetic Semiconductors within Heitler-London Approximation

100%
Bednarski H., Spałek J.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
967-969
EN
We determine the states of a pair of bound magnetic polarons in a diluted magnetic semiconductor by taking into account both the molecular nature of the two-electron wave function in the Heitler-London approximation, as well as the thermodynamic fluctuations of magnetization due to localized 3d spins. We extend the theory of a single bound magnetic polaron to molecular case.
4
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Studies of Optical Properties of Protonated Polyazomethine Thin Films

81%
Bednarski H., Weszka J., Domański M., Cozan V.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
939-941
EN
We report results of experimental studies supplemented with the first principles calculations aimed to explain influence of doping on electronic and optoelectronic properties of thin PPI films. It has been predicted theoretically and confirmed experimentally that chemical doping with the HCl acid vapor is thermally reversible process due to relatively low energy barrier for protonation.
5
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Application of Generalized Pair Approximation to Diluted Magnetic Semiconductor Quantum Structures

81%
Bednarski H., Cisowski J., Portal J.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
723-726
EN
Analysing the d-d interaction in diluted magnetic semiconductor quantum structures, we used our generalized pair approximation which permits to take into account the real spatial distribution of the magnetic ions in diluted magnetic semiconductor layers close to the nonmagnetic quantum well. We subsequently applied our approach to calculate the Zeeman splittings in the CdTe/Cd_{1-x}Mn_{x}Te quantum structures with x=5 and 7.5% and we obtained a good agreement with the experimental results.
6
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Influence of Pressure on Magnetization of (Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2}

71%
Bednarski H., Cisowski J., Lubczyński W., Voiron J., Portal J.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
205-208
EN
The influence of hydrostatic pressure up to 0.6 GPa on magnetization of (Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2} with various compositions was studied at 4.2 K and in magnetic fields up to 7 T. The obtained experimental data were analysed within our generalized pair approximation model, treating the total Mn-Mn interaction strength as a sum of superexchange and the Bloembergen-Rowland exchange. As a result, we obtained satisfactory agree­ment between our approach and experiment by introducing a pressure de­pendence of p-d hybridization potential V_{pd} in the form V_{pd} ∝ d^{-4}, where d is the Mn-As bond length which decreases with pressure.
7
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Magnetic Specific Heat of (Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2}

62%
Bednarski H., Cisowski J., Schmitt D., Voiron J., Portal J., Lubczyński W.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
705-708
EN
The specific heat of (Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2} with low Mn concentration (x ≤ 0.067) and for two Zn contents (y = 0.14 and y = 0.34) has been measured in the temperature range of 1.5-30 K. The magnetic contribution to the total specific heat has been analysed within our generalized pair approximation model which takes into account the complicated tetragonal crystal structure of Cd_{1-x-y}Zn_{y}Mn_{x})_{3}As_{2}. Assuming that the total Mn-Mn interaction strength is a sum of superexchange and the Bloembergen-Rowland exchange, we have obtained a very good agreement between our approach and experiment by using the analytical formulae with only two adjustable parameters, i.e. the first nearest-neighbour exchange constants for both mechanisms which appear to be strongly dependent on Zn content.
8
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Studies of Transport Properties of Single Layer Devices Based on the Polyazomethine Thin Films

62%
Weszka J., Domański M., Jurusik J., Hajduk B., Chwastek M., Bednarski H.
Acta Physica Polonica A
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2011
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vol. 120
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issue 5
936-938
EN
This work reports results of studies on transport properties of single-layer devices based on polyazomethine thin films with different metal electrodes. Recorded I-V characteristics of Au-PPI-Au and Au-PPI-Al structures were analyzed in detail. It appears that I-V characteristics of Au-PPI-Au structures are consistent with the Mott-Gurney law with the mobility value of 2× 10^{-6} cm^2/(V s). Relatively low current in Au-PPI-Al devices is attributed to high value of the Schottky barrier and/or due to low density of longer conjugated segments in polyazomethine thin films.
9
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Stability of Diodes with Poly(3-hexylthiophene) and Polyazomethines Thin Organic Layer

62%
Bednarski H., Gąsiorowski J., Domański M., Hajduk B., Jurusik J., Jarząbek B., Weszka J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1083-1086
EN
Herein we report results of studies on stability of diodes based on organic semiconductors such as poly (3-hexylthiophene) (P3HT) and soluble derivative of polyazomethine poly(1,4-(2,5-bisoctyloxy phenylenemethylidynenitrilo)-1,4-phenylenenitrilomethylidyne), (BOO-PPI). Both polymers were deposited on glass/ITO substrate with or without covering with blocking layer: poly(3,4-ethylenedioxythiophene):poly(4-styrene sulfonate) (PEDOT:PSS) and finished with Al back electrode. Prepared devices were studied by monitoring their electrical conductivity under nitrogen atmosphere and ambient air conditions. Under nitrogen atmosphere a marked influence of presence of the blocking layer on the diodes electrical conductivity was revealed. The P3HT diodes prepared without PEDOT:PSS thin film shown quick degradation, whereas presence of these layers stabilizes electrical conductivity in these devices. Inversely, the PPI based diodes without the PEDOT:PSS revealed stable conducting properties, while corresponding diodes with PEDOT:PSS layer showed degradation traces of their conducting properties.
10
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The Influence of PEDOT to PSS Ratio on the Optical Properties of PEDOT:PSS Thin Solid Films - Insight from Spectroscopic Ellipsometry

52%
Bednarski H., Hajduk B., Jurusik J., Jarząbek B., Domański M., Łaba K., Wanic A., Łapkowski M.
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EN
In this work, we study the influence of the PEDOT to PSS ratio on the optical properties of PEDOT:PSS thin solid films using spectroscopic ellipsometry and UV-vis spectrometry. In the data analysis, we develop a consisted composition dependent optical model of PEDOT:PSS. This enabled us to account for contributions from PSS part within the Tauc-Lorentz optical model and from PEDOT part within the Drude-Lorentz optical model. Moreover, we relate the optical properties of PEDOT:PSS thin solid films to their electrical specific conductivities in the frame of the generalized effective medium theory. Determined in this manner electrical conductivities of five commercially available water dispersions of PEDOT:PSS are compared with their nominal values.
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