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Wyszukujesz frazę "Świrkowicz, R." wg kryterium: Autor


Tytuł:
Spin Waves and Temperature Dependence of Magnetization in Nickel Thin Films Covered with Iron and Copper
Autorzy:
Świrkowicz, R.
Tematy:
75.10.Lp
75.30.Ds
75.70.-i
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1929590.pdf  Link otwiera się w nowym oknie
Opis:
Energy spectrum and amplitudes of spin waves, as well as the temperature dependence of the local magnetization in Ni thin films covered with Fe and Cu overlayers are investigated within the framework of the itinerant electron approach. Two acoustic surface modes strongly localized in Fe over-layers are found. Energies of these modes are very close to each other but they are considerably lower than in Ni films with free surfaces. The presence of the strongly localized low-energy modes leads to fast decrease in the surface magnetization as compared to the central layer one. The quasi-linear temperature dependence of the surface magnetization is found whereas the central layer magnetization follows a quasi T$\text{}^{3}\text{}^{/}\text{}^{2}$ law. On the other hand, in films covered with Cu the temperature dependence of the magnetization can be fitted to the Bloch law for all layers. Inside the film the Bloch coefficient weakly depends on the layer index but it rapidly decreases at the surface in the Cu layers.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Dynamic Susceptibility in Thin Films with Antiferromagnetic Coupling between Layers
Autorzy:
Świrkowicz, R.
Tematy:
75.10.Lp
75.30.Cr
75.30.Ds
75.50.Ee
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1952834.pdf  Link otwiera się w nowym oknie
Opis:
The dynamic susceptibility of the system with antiferromagnetic coupling between layers is investigated within the framework of the multiband model using the equation of motion with random phase approximation. Calculations are performed in the mixed Bloch-Wannier representation and a general form for χ is found. The susceptibility can be written in terms of two-particle Green's functions expressed in the local coordinate system with the z axis aligned along the local magnetization. The expression depends on an angle between the magnetization direction in a given layer and the crystal axis. Preliminary numerical calculations are performed for two systems: ultrathin Cr film and Fe/Cr multilayer structure. Imaginary part of the susceptibility corresponding to different layers is calculated and spin waves are discussed.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Ground-State Properties and Spin Waves in Ultrathin Fe Films Covered with Magnetic and Nonmagnetic Materials
Autorzy:
Świrkowicz, R.
Tematy:
75.30.Ds
75.70.-i
75.10.Lp
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1933591.pdf  Link otwiera się w nowym oknie
Opis:
Properties of ultrathin films consisted of 5 and 7 atomic layers of Fe and covered with magnetic (Co) or nonmagnetic (Cu, Ag) materials are investigated within the framework of the multiband model. Ground-state results consistent with those known from ab initio approaches are obtained. Spin waves are studied in the random phase approximation with the use of the susceptibility method. Amplitudes and dispersion relations are calculated. Two acoustic modes with amplitudes enhanced at the interface are found.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Temperature Dependence of Magnetization in Transition Metal Ultrathin Films of Various Thicknesses
Autorzy:
Świrkowicz, R.
Tematy:
75.70.Ak
76.80.+y
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1891839.pdf  Link otwiera się w nowym oknie
Opis:
Temperature dependence of the local magnetization in the spin-wave regime is calculated within the framework of the multiband model for ultrathin films consisting of 5, 7 and 9 monolayers. The temperature range in which the calculated results can be fitted to the Bloch T$\text{}^{3}$ $\text{}^{/}$ $\text{}^{2}$ law is found in all cases. The Bloch coefficient Bay corresponding to temperature dependence of the average film magnetization is found to be proportional to 1/D, where D is the thickness of the film. The spatial distribution of the local magnetization is obtained. The Bloch coefficient corresponding to the surface layer appears to be greater than the one corresponding to the central layer, namely B$\text{}_{s}$ > B$\text{}_{c}$. The ratio B$\text{}_{s}$/B$\text{}_{c}$ is increasing with an increase of the film thickness. The calculated results are well consistent with experimental ones obtained for ultrathin films of various thicknesses.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electrical and Heat Currents in Nanoscopic System with Ferromagnetic Electrodes of Non-Collinear Magnetic Moments
Autorzy:
Wierzbicki, M.
Świrkowicz, R.
Tematy:
73.23.Hk
73.50.Lw
85.80.Fi
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/1426962.pdf  Link otwiera się w nowym oknie
Opis:
Thermoelectric properties of nanoscopic system composed of a single-level quantum dot attached to ferromagnetic electrodes are studied with the use of the non-equilibrium Green function formalism. Electrical and heat currents flowing through the system under temperature gradient and bias voltage are calculated in the non-linear regime. Both charge and heat currents strongly depend on configuration of magnetic moments in the leads. TMR ratio is mostly positive, but in a region of small bias voltages, where the electron flow is determined by the temperature gradient, electrical current in parallel and antiparallel configurations flows in opposite directions leading to considerable negative TMR.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electronic Transport through the Double-Dot System
Autorzy:
Świrkowicz, R.
Sztenkiel, D.
Tematy:
75.20.Hr
72.15.Qm
72.25.-b
73.23.Hk
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/2038086.pdf  Link otwiera się w nowym oknie
Opis:
Electron tunnelling through two quantum dots in series is theoretically studied. A limit of intermediate coupling between the dots is considered. The non-equilibrium Green function formalism is used to calculate electric current and mean number of electrons accumulated on the dots. Lesser and retarded Green functions are calculated in the Hartree-Fock approximation with the use of the equation of motion method. Current flowing through the system calculated in dependency on gate voltages shows two resonant peaks, each peak with two additional shoulders. I-V characteristics and differential conductance in a resonance and out of resonance cases are calculated and discussed.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Spin-Polarized Current in Coulomb Blockade and Kondo Regime
Autorzy:
Ogrodnik, P.
Świrkowicz, R.
Tematy:
73.23.-b
73.21.La
85.75.-d
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/2047683.pdf  Link otwiera się w nowym oknie
Opis:
Spin-polarized electron transport through a single-level quantum dot attached to ferromagnetic and non-magnetic leads is studied with the use of the non-equilibrium Green function technique. Current polarization is investigated in dependence on parameters which characterize the device: the lead's polarization, a position of the dot energy level compared to the Fermi level in electrodes, and the Zeeman splitting of the dot level in an external magnetic field applied to the dot. Calculations were performed in two transport regimes: the Coulomb blockade regime with correlation effects treated within the Hartree-Fock approximation and the Kondo regime with a more rigorous approach to many-body effects at low temperatures.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electron Transport through Double Quantum Dot: from SU(4) Kondo to SU(2) Symmetry
Autorzy:
Sztenkiel, D.
Świrkowicz, R.
Tematy:
73.63.Kv
72.15.Qm
73.40.Gk
73.23.Hk
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Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/2047706.pdf  Link otwiera się w nowym oknie
Opis:
Electron transport across two capacitively coupled quantum dots in a parallel geometry is theoretically studied in the non-linear response regime with spin and orbital degrees of freedom taken into account and the Kondo effect induced by on-site and inter-dot Coulomb correlations is analyzed. For a system with each dot symmetrically coupled to a separate set of electrodes a well-defined spin and orbital contributions to zero-bias Kondo resonance are obtained. The Kondo peak splits if spin and/or orbital degeneracies are removed. A suppression of the orbital Kondo anomaly due to orbital asymmetry and channel mixing effects is discussed.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electron Transport through Double Quantum Dots with Interdot Coulomb Repulsion
Autorzy:
Sztenkiel, D.
Świrkowicz, R.
Tematy:
73.23.-b
73.21.La
73.23.Hk
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/2047016.pdf  Link otwiera się w nowym oknie
Opis:
Electron transport through a system of two quantum dots connected in series is studied theoretically with the use of non-equilibrium Green function formalism based on the equation of motion method. Each dot is described by the one-level Anderson Hamiltonian and interdot Coulomb interactions in the form of the Hubbard-like term are taken into account. The electric current and occupation numbers are calculated with the use of two different approaches. The results of the methods are compared and discussed in detail. Strong asymmetry of I-V characteristics with respect to bias voltage reversal are obtained when energy levels of the dots are not aligned.
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Electron Transport through Double Quantum Dot System with Inter-Dot Coulomb Interaction
Autorzy:
Sztenkiel, D.
Świrkowicz, R.
Tematy:
73.23.-b
73.21.La
73.23.Hk
Pokaż więcej
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Powiązania:
https://bibliotekanauki.pl/articles/2047295.pdf  Link otwiera się w nowym oknie
Opis:
A theoretical approach to a problem of electron transport through double quantum dot systems based on non-equilibrium Green function formalism using equation of motion method is presented. I-V characteristics and differential conductance are calculated and discussed in detail in the intermediate regime with tunneling rate between the quantum dots comparable to coupling constants with external electrodes. Effects of inter-dot Coulomb correlations are studied for various values of interaction parameter U. It is shown that the interaction influences transport properties in a pronounced way and apart from the simple Coulomb blockade additional effects can be obtained. When energy levels of two quantum dots are not aligned, the asymmetry in conductance characteristics is closely related to a voltage dependence of population numbers in both quantum dots. For a one bias polarization electrons are well localized in quantum dots in a low voltage region, whereas for the opposite one they are partly delocalized.
Dostawca treści:
Biblioteka Nauki
Artykuł

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