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1
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The Seebeck Effect in Double Tunnel Junctions with Ferromagnetic Electrodes and Central Layer Separated by Nonmagnetic Barriers

100%
Wilczyński M.
Acta Physica Polonica A
|
2018
|
vol. 133
|
issue 3
544-547
EN
The Seebeck effect is analysed in the double planar tunnel junctions consisting of ferromagnetic electrodes and the central layer separated by nonmagnetic barriers with the arbitrary angle between magnetic moments in neighbouring ferromagnetic layers. The Seebeck coefficient is calculated as a function of the thickness of the central layer. The influence of temperature of the junction and the relative orientation of magnetic moments in ferromagnetic layers on this coefficient is also analysed. Calculations are performed in the linear response theory using the free-electron model. It has been found that the Seebeck coefficient oscillates with the thickness of the central layer and can be strongly enhanced in the junction with special central layer thickness due to electron tunnelling by resonant states. The form of the observed oscillations depends on the temperature of the junction. The magnitude of the Seebeck coefficient usually increases with the increase of the angle between magnetic moments in the neighbouring ferromagnetic layers as in the case of single junctions. However, in the junctions with the specially designated central layer the decrease of the magnitude of the Seebeck coefficient with the increase of this angle can be observed.
2
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Thermoelectric Effects in Planar Tunnel Junctions

100%
Wilczyński M.
Acta Physica Polonica A
|
2012
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vol. 121
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issue 5-6
1188-1190
EN
The thermopower and the charge current generated by the finite temperature gradient applied to ferromagnetic planar tunnel junctions are investigated in the spin-polarized free-electron-like one-band model. It has been shown that the current depends almost linearly on the temperature difference between the electrodes while the thermopower does not depend significantly on the temperature gradient. The studied quantities depend on the magnetic configuration of the junction. The form of this dependence is sensitive to the height of the barrier, but is not sensitive to the temperature difference between the electrodes.
3
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Tunneling Magnetoresistance in Planar Ferromagnetic Junctions

64%
Wilczyński M., Barnaś J.
Acta Physica Polonica A
|
2000
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vol. 97
|
issue 3
443-446
EN
Bias dependence of the tunnel magnetoresistance in simple planar ferromagnetic junctions is considered theoretically within the one-band model. The limit of sequential tunnelling in double junctions with a non-magnetic central electrode is studied as well. In this case tunnel magnetoresistance exists only when the spin relaxation time due to spin-flip scattering processes inside the central electrode is sufficiently long.
4
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Electronic Properties and Dynamic Susceptibility of MnTe Systems

64%
Wilczyński M., Świrkowicz R.
Acta Physica Polonica A
|
1997
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vol. 92
|
issue 5
1048-1050
EN
Thin MnTe films are investigated. Electronic structure, local density of states and local magnetic moments are calculated for systems with ferromagnetic and antiferromagnetic order. Spin-dependent modifications of the density of states near the surface are results of the changes in p-d hybridization. Magnetic longitudinal and dielectric susceptibilities are calculated.
5
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Phonon-Assisted Kondo Resonance in Spin-Dependent Transport through a Quantum Dot

51%
Świrkowicz R., Wilczyński M., Barnaś J.
Acta Physica Polonica A
|
2009
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vol. 115
|
issue 1
272-274
EN
Effects of local vibrational modes on electron transport through a quantum dot attached to ferromagnetic electrodes are studied in the Kondo regime by the non-equilibrium Green function formalism based on the equation of motion method. Differential conductance is calculated for parallel and antiparallel configurations of the leads' magnetic moments, and well defined Kondo resonance peaks and their phonon satellites are found. The influence of a compensating magnetic field on the peak positions is also discussed.
6
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Spin Torque in Double Planar Tunnel Junctions

51%
Wilczyński M., Świrkowicz R., Barnaś J.
Acta Physica Polonica A
|
2009
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vol. 115
|
issue 1
269-271
EN
Transport in a double planar tunnel junction with ferromagnetic electrodes is analyzed theoretically in the zero-temperature limit. The in-plane and out-of-plane components of the spin torque exerted on magnetic moment of the central layer are determined as a function of the angle θ between magnetic moments of one of the external electrodes and of the central layer. Two configurations of the magnetic moments of external electrodes are considered, i.e. parallel and antiparallel ones. It is found that both torque components depend strongly on the thickness of the central layer, especially in junctions with a relatively thin central layer, where enhancement of the torque or a change of its sign can be observed for specific layer thicknesses. In junctions with thick central layer and in the limit of small bias voltage applied to the junction, the in-plane torque is generally smaller in the parallel configuration than in the antiparallel one. The opposite relation is observed for the normal torque.
7
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Spin Torque in Semiconductor Single Planar Tunnel Junctions

51%
Wilczyński M., Barnaś J., Świrkowicz R.
Acta Physica Polonica A
|
2008
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vol. 113
|
issue 1
35-38
EN
Transport in a single planar tunnel junction with electrodes made of a ferromagnetic semiconductor is analyzed theoretically in the zero- -temperature limit. Tunneling current and both (in-plane and out-of-plane) components of the spin torque exerted on one of the ferromagnetic electrodes are determined as a function of the angle\thet a between magnetic moments of the electrodes. The influence of the bias voltage and spin splitting of the electron band (in both electrodes) on the spin torque components is analyzed numerically.
8
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Content available

Nonequilibrium Kondo Effect in a Single-Channel Quantum Dot Asymmetrically Coupled to Two Ferromagnetic Reservoirs

51%
Świrkowicz R., Wilczyński M., Barnaś J.
Acta Physica Polonica A
|
2004
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vol. 105
|
issue 1-2
149-154
EN
Nonequilibrium Kondo effect in a quantum dot asymmetrically coupled to two ferromagnetic metallic leads is analyzed theoretically. The nonequilibrium Green function technique is used to calculate density of states and electric current. The lesser and retarded (advanced) Green functions are calculated by the equation of motion method within a consistent approximation scheme. The case where one electrode is half-metallic is analyzed numerically in details.
9
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Poor Man's Scaling and Green Function Analysis of the Kondo Anomaly in Single-Level Quantum Dots

51%
Wawrzyniak M., Świrkowicz R., Wilczyński M., Barnaś J.
Acta Physica Polonica A
|
2008
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vol. 113
|
issue 1
553-556
EN
Kondo effect in a single-level quantum dot attached to magnetic leads is studied theoretically by the "poor man's scaling" and non-equilibrium Green function methods. From the scaling equations we derive the Kondo temperature as a function of the model parameters - in particular as a function of the angle between magnetic moments. Transport characteristics, i.e. differential conductance and tunnel magnetoresistance associated with magnetization rotation, were calculated within the non-equilibrium Green function formalism based on the equation of motion method.
10
Content available remote

Electronic Transport through a Quantum Dot Coupled to Non-Collinear Ferromagnetic Electrodes: The Kondo Regime

51%
Świrkowicz R., Wilczyński M., Wawrzyniak M., Barnaś J.
Acta Physica Polonica A
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2008
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vol. 113
|
issue 1
565-568
EN
Linear and non-linear conductance of quantum dots attached to magnetic leads is considered theoretically in the Kondo regime. The considerations are based on the non-equilibrium Green function formalism and the relevant equation of motion method. Splitting of the Kondo anomaly due to coupling of the dot to ferromagnetic electrodes, and its dependence on magnetic configuration of the system and on the lead's spin polarization is studied numerically.
11
Content available remote

Diffusive Propagation of Phonon Beams in Yttrium Aluminum Garnets Containing Substitutional Rare Earth Atoms

45%
Ivanov S., Khazanov E., Paszkiewicz T., Taranov A., Wilczyński M.
Acta Physica Polonica A
|
1995
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vol. 87
|
issue 2
381-386
EN
The diffusive maxima of phonon signals are studied for a number of solid solutions of rare earth atoms in yttrium aluminum garnets. The used exact formula for the diffusion constants allows for qualitative discussion of the obtained results. The established energy of phonons, forming the diffusive maximum of phonon signal of the temperature T_{H} arriving at the bolometer, ranges from 3.2k_{B}T_{H} to 4.2k_{B}T_{H}, which is in reasonable agreement with the existing estimations. The qualitative analysis allows us to estimate the contribution, made by the rare earth ions occupying the octahedral positions of the sixfold oxygen coordination, to the scattering of phonons due to lattice imperfections in yttrium aluminum garnets.
12
Publication available in full text mode
Content available

Spin Polarized Transport through Quantum Dots: Coulomb Blockade and Kondo Effect

39%
Barnaś J., Świrkowicz R., Wilczyński M., Weymann I., Martinek J., Dugaev V.
Acta Physica Polonica A
|
2003
|
vol. 104
|
issue 2
165-177
EN
Spin related effects in electronic transport through quantum dots, coupled via tunneling barriers to two metallic leads, are discussed from the point of view of fundamental physics and possible applications in spin electronics. The effects follow either from long spin relaxation time in the dots or from spin dependent tunneling through the barriers when the external leads are ferromagnetic. In the former case large nonequilibrium spin fluctuations in the dot can be induced by flowing current. These fluctuations modify transport characteristics, particularly the shape of the Coulomb steps. In the latter case electric current depends on magnetic configuration of the system, and tunnel magnetoresistance effect due to magnetization rotation can occur. Transport properties in the weak coupling regime are described perturbatively in the first (sequential) and second (cotunneling) orders. In the strong coupling regime, on the other hand, the equation of motion for nonequilibrium Green functions is used to calculate electric current at low temperatures, where the Kondo peak in conductance is formed in the zero bias regime. In symmetrical systems the Kondo peak is split in the parallel magnetic configuration, whereas no splitting occurs for the antiparallel alignment. Theoretical results are discussed in view of available experimental data.
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