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    Wyświetlanie 1-8 z 8
    Tytuł:
    Magnetoresistance and Magnetic Properties of the Double Perovskites
    Autorzy:
    Philipp, J. B.
    Majewski, P.
    Reisinger, D.
    Geprägs, S.
    Opel, M.
    Erb, A.
    Alff, L.
    Gross, R.
    Powiązania:
    https://bibliotekanauki.pl/articles/2037043.pdf
    Data publikacji:
    2004
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.50.-y
    75.50.Cc
    75.50.Ss
    Opis:
    The magnetic double perovskite materials of composition A$\text{}_{2}$BB'O$\text{}_{6}$ with A an alkaline earth ion and B and B' a magnetic and non-magnetic transition metal or lanthanide ion, respectively, have attracted considerable attention due to their interesting magnetic properties ranging from antiferromagnetism to geometrically frustrated spin systems and ferromagnetism. With respect to application in spin electronics, the ferromagnetic double perovskites with BB'= CrW, CrRe, FeMo, or FeRe and A = Ca, Ba, Sr are highly interesting due to their in most cases high Curie temperatures well above room temperature and their half-metallic behavior. Here, we summarize the structural, magnetotransport, magnetic, and optical properties of the ferromagnetic double perovskites and discuss the underlying physics. In particular, we discuss the impact of steric effects resulting in a distorted perovskite structure, doping effects obtained by a partial replacing of the divalent alkaline earth ions on the A site by a trivalent lanthanide as well as B/B' cationic disorder on the Curie temperature T$\text{}_{C}$, the saturation magnetization and the magnetotransport properties. Our results support the presence of a kinetic energy driven mechanism in the ferromagnetic double perovskites, where ferromagnetism is stabilized by a hybridization of states of the non-magnetic B'-site positioned in between the high spin B-sites.
    Źródło:
    Acta Physica Polonica A; 2004, 105, 1-2; 7-26
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Pressure Dependence of Elastic Constants in Zinc-Blende III-N and Their Influence on the Light Emission in Nitride Heterostructures
    Autorzy:
    Łepkowski, S. P.
    Majewski, J. A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2038098.pdf
    Data publikacji:
    2004-06
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    62.20.Dc
    62.50.+p
    Opis:
    We studied the nonlinear elasticity effects for the case of III-N compounds. Particularly, we determined the pressure dependences of elastic constants, in zinc-blende InN, GaN, and AlN by performing ab initio calculations in the framework of plane-wave pseudopotential implementation of the density-functional theory. We found significant and almost linear increase in C$\text{}_{11}$, C$\text{}_{12}$ with pressure for considered nitrides compounds. Much weaker dependence on pressure was observed for C$\text{}_{44}$. We also discussed pressure dependences of two-dimensional Poisson's ratio and elastic anisotropy coefficient. Finally, we showed that the pressure dependence of elastic constants results in significant reduction of the pressure coefficient of the energy emission in cubic InGaN/GaN quantum wells and essentially improves the agreement between experimental and theoretical values.
    Źródło:
    Acta Physica Polonica A; 2004, 105, 6; 559-566
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Effects of Nonlinear Elasticity and Electromechanical Coupling on Optical Properties of InGaN/GaN and AlGaN/AlN Quantum Wells
    Autorzy:
    Łepkowski, S. P.
    Majewski, J. A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2046928.pdf
    Data publikacji:
    2006-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.67.De
    62.20.Dc
    77.65.-j
    Opis:
    We present theoretical studies of effects of the nonlinear elasticity and the electromechanical coupling on the optical properties of InGaN/GaN and AlGaN/AlN quantum wells. In these structures, due to the lattice misfit between constituents, the quantum wells are compressively strained and the intrinsic hydrostatic pressure is present. Therefore, the nonlinear elasticity is investigated by taking into account the pressure dependence of elastic stiffness tensor for the strained quantum wells. We show that this effect leads to (i) decrease in the volumetric strain and (ii) increase in the polarization-induced built-in electric field in the quantum wells. Consequently, the interband transition energies in the quantum wells decrease when the nonlinear elasticity of nitrides is considered. On the other hand, we show that the effect of electromechanical coupling, i.e., co-existence of ordinary and converse piezoelectric effects results in increase in the interband transition energies in the considered quantum wells. It turns out that the influence of the nonlinear elasticity on the optical properties is stronger than the influence of electromechanical coupling for InGaN/GaN quantum wells, while for AlGaN/GaN the opposite situation is observed.
    Źródło:
    Acta Physica Polonica A; 2006, 110, 2; 237-242
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Bands, Bonds, and Polarizations in Nitrides - from Electronic Orbitals to Electronic Devices
    Autorzy:
    Majewski, J. A.
    Zandler, G.
    Vogl, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/2027476.pdf
    Data publikacji:
    2001-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.40.Kp
    77.65.Ly
    Opis:
    A key property of the nitrides is the fact that they possess large spontaneous and piezoelectric polarization fields that allow a significant tailoring of the carrier dynamics and optical properties of nitride devices. In this paper, based on first-principles calculations of structural and electronic properties of bulk nitrides and their heterostructure, we investigate the potential of this novel material class for modern device applications by performing self-consistent Monte Carlo simulations. Our studies reveal that the nitride based electronic devices have characteristics that predispose them for high power and high frequency applications. We demonstrate also that transistor characteristics are favorably influenced by the internal polarization induced electric fields.
    Źródło:
    Acta Physica Polonica A; 2001, 100, 2; 249-260
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Stability and Band Offsets of Heterovalent SiC/GaN Interfaces
    Autorzy:
    Städele, M.
    Majewski, J. A.
    Vogl, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/1934004.pdf
    Data publikacji:
    1995-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    68.35.Fx
    73.20.Dx
    Opis:
    We present first-principles calculations of structural and electronic properties of heterovalent SiC/GaN [001] interfaces. We have investigated interfaces consisting of one and two mixed layers with lateral c(2 × 2), 2 × 1, 1 × 2, 2 × 2 arrangements. Abrupt polar [001] interfaces are energetically unstable with respect to reconstruction. The preferred bonding configurations are found to be Si-N and Ga-C, which correspond to cation-anion bonding. The valence band offsets of the energetically most favorable structures are 1.39 eV for the interface with a mixed Ga/Si layer and 0.45 eV with a mixed C/N layer, with the top of the valence band lying higher in SiC.
    Źródło:
    Acta Physica Polonica A; 1995, 88, 5; 917-920
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ferromagnetism in Cr-Based Diluted Magnetic Semiconductors
    Autorzy:
    Blinowski, J.
    Kacman, P.
    Majewski, J. A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1933725.pdf
    Data publikacji:
    1995-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.70.Gm
    75.50.Pp
    75.50.Dd
    Opis:
    It has been recently established that in zinc chalcogenides with Cr$\text{}^{2+}$ paramagnetic ions the p-d interactions are ferromagnetic. We clarify the origins of this property and make predictions concerning other Cr-based diluted magnetic semiconductors. The observation of the ferromagnetic p-d interaction resuscitated hopes for ferromagnetic d-d exchange interactions in diluted magnetic semiconductors. We have calculated the nearest-neighbor superexchange integrals in Cr-based diluted magnetic semiconductors. No simple correlation between the signs of p-d and d-d interactions has been found. Still, there are extended energy regions where the calculated superexchange is ferromagnetic and the act ual parameters of DMS with Cr$\text{}^{2+}$ seem to match these regions.
    Źródło:
    Acta Physica Polonica A; 1995, 88, 4; 683-686
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Nonlinear Elasticity in Wurtzite GaN/AlN Planar Superlattices and Quantum Dots
    Autorzy:
    Łepkowski, S. P.
    Majewski, J. A.
    Jurczak, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/2044495.pdf
    Data publikacji:
    2005-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.67.-n
    62.20.Dc
    62.50.+p
    Opis:
    The elastic stiffness tensors for wurtzite GaN and AlN show a significant hydrostatic pressure dependence, which is the evidence of nonlinear elasticity of these compounds. We have examined how pressure dependence of elastic constants for wurtzite nitrides influences elastic and piezoelectric properties of GaN/AlN planar superlattices and quantum dots. Particularly, we show that built-in hydrostatic pressure, present in both quantum wells of the GaN/AlN superlattices and GaN/AlN quantum dots, increases significantly by 0.3-0.7 GPa when nonlinear elasticity is used. Consequently, the compressive volumetric strain in quantum wells and quantum dots decreases in comparison to the case of the linear elastic theory. However, the z-component of the built-in electric field in the quantum wells and quantum dots increases considerably when nonlinear elasticity is taken into account. Both effects, i.e., a decrease in the compressive volumetric strain as well as an increase in the built-in electric field, decrease the band-to-band transition energies in the quantum wells and quantum dots.
    Źródło:
    Acta Physica Polonica A; 2005, 108, 5; 749-754
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Modeling of Semiconductor Nanostructures with nextnano$\text{}^{3}$
    Autorzy:
    Birner, S.
    Hackenbuchner, S.
    Sabathil, M.
    Zandler, G.
    Majewski, J. A.
    Andlauer, T.
    Zibold, T.
    Morschl, R.
    Trellakis, A.
    Vogl, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/2046896.pdf
    Data publikacji:
    2006-08
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    73.43.Cd
    73.21.Fg
    73.61.Ey
    77.65.Ly
    85.30.Tv
    73.40.Mr
    Opis:
    nextnano$\text{}^{3}$ is a simulation tool that aims at providing global insight into the basic physical properties of realistic three-dimensional mesoscopic semiconductor structures. It focuses on quantum mechanical properties such as the global electronic structure, optical properties, and the effects of electric and magnetic fields for virtually any geometry and combination of semiconducting materials. For the calculation of the carrier dynamics a drift-diffusion model based on a quantum-mechanically calculated density is employed. In this paper we present an overview of the capabilities of nextnano$\text{}^{3}$ and discuss some of the main equations that are implemented into the code. As examples, we first discuss the strain tensor components and the piezoelectric effect associated with a compressively strained InAs layer for different growth directions, secondly, we calculate self-consistently the quantum mechanical electron density of a Double Gate MOSFET, then we compare the intersubband transitions in a multi-quantum well structure that have been obtained with a single-band effective mass approach and with an 8-band k·p model, and finally, we calculate the energy spectrum of a structure in a uniform magnetic field.
    Źródło:
    Acta Physica Polonica A; 2006, 110, 2; 111-124
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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