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1
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Kinetic Exchange in Diluted Magnetic Semiconductors of Wurtzite Structure

100%
Blinowski J., Kacman P.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
693-696
EN
Kinetic exchange between valence electrons and paramagnetic ions in diluted magnetic semiconductors of wurtzite structure is examined and compared with the results obtained previously for zinc-blende type diluted magnetic semiconductors. Two limiting electron configurations of the impurity ion, d^{5} and d^{1}, are discussed. For the former, it is shown that the exchange constant anisotropy, experimentally observed in CdMnSe, results from the anisotropy of the hybridization matrix elements. In the latter case, apart from the similar anisotropy of the ferromagnetic exchange constant, additional, antiferromagnetic corrections should be expected, since for this particular symmetry the hybridization between the ground state of the ion and valence band becomes allowed.
2
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Spin-Dependent Phenomena in (Ga,Mn)As Heterostructures

100%
Sankowski P., Kacman P.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
139-150
EN
A model for spin-dependent tunneling in semiconductor heterostructures, which combines a multi-orbital empirical tight-binding approach with a Landauer-Büttiker formalism, is presented. Using this approach we explain several phenomena observed in modulated structures of (Ga,Mn)As, i.e., large values of the electron current spin polarization in magnetic Esaki- Zener diode and the high tunneling magnetoresistance ratio. Next, the relevance of this theory to assess the tunneling anisotropic magnetoresistance effect is studied. The results of applying the tight-binding model to describe the recently observed interlayer exchange coupling in (Ga,Mn)As-based superlattices are also shown.
3
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Double Exchange in Mixed-Valency Diluted Magnetic Semiconductors

100%
Blinowski J., Kacman P.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
731-734
EN
The role of double-exchange, a non-Heisenberg spin-spin interaction between the magnetic ions of identical chemical nature but different charge states, in the mixed-valency diluted magnetic semiconductors is discussed. The mechanism correlates the spins of magnetic ions by virtual hopping of a d-electron from one ion to the other via the p-band states. We calculate the energy spectrum for pairs of magnetic ions within the charged ionic clusters stabilized by the charge-charge correlations, taking into account simultaneously both the double and the superexchange. The ferromagnetic, non-Heisenberg double exchange might compete with the Heisenberg-like, ferrimagnetic superexchange, thus resulting in canted alignments of ionic spins.
4
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Superexchange in A^{II}B^{VI} Diluted Magnetic Semiconductors with Mn, Fe and Co Ions

100%
Blinowski J., Kacman P.
Acta Physica Polonica A
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1995
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vol. 87
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issue 2
539-542
EN
A theory of superexchange, the dominant ion-ion spin interaction, for Mn-, Fe- and Co-based DMS is presented. The theory takes into account the band structure of A^{II}B^{VI} compounds, the orbital dependence of the hybridization and the intra shell correlations of the d-electrons, which are essential in the case of the non-S-state ions. The general formulae relating the superexchange to the band structure and the ionic energy spectrum were obtained - the dominant part of the superexchange turns out to be inversely proportional to the square of the ionic spin. This explains the observed in­crease in the average values of d-d exchange constants, when passing from Mn via Fe to Co ions in DMS.
5
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Pecularities of p-d Interaction in Semimagnetic Semiconductors with Cr^{2+1}

100%
Blinowski J., Kacman P.
Acta Physica Polonica A
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1991
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vol. 80
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issue 2
295-297
EN
In cubic DMS crystals with Cr^{2+} content the non-Heisenberg part of the p-d interaction together with the strong, static Jahn-Teller effect may lead to a zero-magnetic field splitting and significant modifications of the spin splittings for the valence band. The effect reaches a maximum when all Jahn-Teller distortions are oriented along one of the [100]-type crystallographic directions.
6
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On the Kinetic Exchange in A^{III}B^V Diluted Magnetic Semiconductors

100%
Blinowski J., Kacman P.
Acta Physica Polonica A
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2001
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vol. 100
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issue 3
343-349
EN
In the case of II-VI diluted magnetic compounds it was shown that the kinetic exchange mechanism depends crucially on the electronic configuration of the magnetic ions and the charge transfer energies for the transitions from the band onto the magnetic ion and vice versa. In the present paper we analyze these effects in the family of III-V diluted magnetic semiconductors, showing that they affect considerably the predictions of the values of the Curie temperature and should be taken into account in the search for room temperature ferromagnetism in diluted magnetic semiconductors.
7
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Spin-Dependent Interaction of a Band Electron with Paramagnetic Impurities

100%
Blinowski J., Kacman P.
Acta Physica Polonica A
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1991
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vol. 79
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issue 1
145-148
EN
A band electron interacting with N electrons in a d-shell of a paramagnetic impurity in zinc-blende type semiconductors was considered. The hybridization of band and d-states in the crystal field and the nonorthogonality mechanisms of interaction were examined in addition to the standard direct exchange. The Heisenberg-type form was derived for the interaction between a Γ_8-electron and an impurity with a half-filled d-shell. The domination of the hybridization mechanism explains the observed sign of the effective exchange constant for Γ_8 electrons in diluted magnetic semiconductors (DMS) and the difference in magnitude of this constant for Mn^{2+} and Fe^{3+} ions in HgSe.
8
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Correlations in Magnetic-Nonmagnetic Semiconductor Superlattices - Simple Model

100%
Blinowski J., Kacman P.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
719-723
EN
The magnetic interactions in superlattices formed by alternating layers of magnetic and nonmagnetic semiconductors with common anions were studied theoretically. Within a one-dimensional tight-binding model by minimising the total electronic energy we show the existence of an efficient long range mechanism of magnetic correlations between the neighbouring magnetic layers in such superlattices. The cases of magnetic ions in the barriers (e.g., EuTe/PbTe) and in the wells, with the order within the magnetic layers being either ferromagnetic or antiferromagnetic, have been considered and compared with the paramagnetic case. In the case of antiferromagnetic ordering within magnetic layers we have found that for even and odd numbers of magnetic monolayers different magnetic superlattices are energetically favourable.
9
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Interlayer Coupling in EuS-Based Superlattices (Dependence on the Energy Structure of Non-Magnetic Layer)

100%
Sankowski P., Kacman P.
|
EN
The interlayer coupling between ferromagnetic EuS layers separated by spacer layers of diamagnetic insulators, YbSe and SrS, is studied within a 3D tight-binding model. The dependencies of the coupling strength on the energy structure of the spacer, on strains resulting from the lattice mismatch between the superlattice constituents, as well as on an applied hydrostatic pressure and lattice deformations, are presented. The sign and the range of the obtained coupling agree with the behavior of magnetic correlations observed recently in neutron reflectivity spectra of EuS/YbSe superlattices.
10
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The Ferromagnetic p-d Exchange in Diluted Magnetic Semiconductors

81%
Blinowski J., Dietl T., Kacman P.
Acta Physica Polonica A
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1992
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vol. 82
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issue 4
641-644
EN
The antiferromagnetic type of the interaction between the Γ_{8}-band electrons and the Mn^{2+} ions in A^{II}B^{IV} diluted magnetic semiconductors has been explained by invoking the p-d hybridization mechanism. In this paper it is shown that for particular electronic configurations of the magnetic ions in diluted magnetic semiconductors the p-d hybridization can lead to a ferromagnetic interaction between the valence-band electrons and the localized spins. This happens when all the one-electron d-orbitals which hybridize with p-band states are empty (e.g., as in Sc^{2+} and Ti^{2+} ions). The appropriate p-d Hamiltonian is derived and the ferromagnetic exchange constants are evaluated.
11
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Ferromagnetism in Cr-Based Diluted Magnetic Semiconductors

81%
Blinowski J., Kacman P., Majewski J.
Acta Physica Polonica A
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1995
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vol. 88
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issue 4
683-686
EN
It has been recently established that in zinc chalcogenides with Cr^{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^{2+} seem to match these regions.
12
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Quantum Spin Hall Effect in Strained (111)-Oriented SnSe Layers

81%
Safaei S., Galicka M., Kacman P., Buczko R.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1a
A-150-A-152
EN
Recently, the quantum spin Hall effect has been predicted in (111)-oriented thin films of SnSe and SnTe topological crystalline insulators. It was shown that in these films the energy gaps in the two-dimensional band spectrum depend in an oscillat ory fashion on the layer thickness - the calculated topological invariant indexes and edge state spin polarizations show that for films 20-40 monolayers thick a two-dimensional topological insulator phase appears. Edge states with the Dirac cones with opposite spin polarization in their two branches are obtained for both materials. However, for all but the (111)-oriented SnTe films with an even number of monolayers an overlapping of bands in Γ̅ and M̅ diminishes the final band gap and the edge states appear either against the background of the bands or within a very small energy gap. Here we show that this problem in SnSe films can be removed by applying an appropriate strain. This should enable observation of the quantum spin Hall effect also in SnSe layers.
13
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Modeling of Small Diameter Semiconductor Nanowires

81%
Bukała M., Galicka M., Buczko R., Kacman P.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
425-430
EN
The properties of very thin (up to 16Å diameter) wires, cut out from the bulk in either zinc-blende or wurtzite material, are studied theoretically. In the total energy calculations we use ab initio methods and consider three different crystallographic growth axes for the zinc-blende and one for the wurtzite structure. We show that the most stable zinc-blende nanowires are those growing along (111) direction, however, the wurtzite structure is found to be energetically more favorable than the zinc-blende for wires of the same diameter. In addition, the band structure of the wires was calculated.
14
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Interlayer Coupling in EuS-Based Superlattices Deduced from Neutron Scattering Experiments

62%
Sankowski P., Kępa H., Kacman P., Sipatov A., Majkrzak C., Giebultowicz T.
Acta Physica Polonica A
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2004
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vol. 105
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issue 6
607-614
EN
The ferromagnetic/diamagnetic semiconductor superlattices, EuS/PbS and EuS/YbSe, were studied by neutron reflectivity. In order to determine the strength of the interlayer coupling, the intensity of the first magnetic Bragg peak vs. applied external magnetic field was measured. Additionally, the in-plane anisotropy and the domain structure were studied by polarized neutron reflectivity. The dependence of the intensity of the antiferromagnetic neutron reflectivity peak vs. magnetic field was simulated using a Stoner-Wohlfarth model. To reproduce the observed spectra it was necessary to take into account the presence of fluctuations of the nonmagnetic layers thickness, by assuming a Gaussian spread of the interlayer coupling constant $J$. For both EuS/PbS and EuS/YbSe superlattices, the best fit was obtained for the directions of the in-plane easy axes, which agree with those determined by polarized neutron reflectivity.
15
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Experimental and Theoretical Analysis οf PbTe-CdTe Solid Solution Grown by Physical Vapour Transport Method

42%
Szot M., Szczerbakow A., Dybko K., Kowalczyk L., Smajek E., Domukhovski V., Łusakowska E., Dziawa P., Mycielski A., Story T., Bukała M., Galicka M., Sankowski P., Buczko R., Kacman P.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
959-961
EN
Bulk monocrystals of Pb_{1-x}Cd_{x}Te, with the Cd content x up to 0.11, were grown by physical vapour transport method. The structural, electrical and optical properties of these ternary crystals were studied experimentally and theoretically. All investigated samples exhibit rock-salt structure and high crystal quality, which was confirmed by X-ray rocking curve width parameter of about 100 arcsec. The decrease of the lattice parameter with increasing Cd content x was found experimentally, in agreement with ab initio calculations. The band structures of Pb_{1-x}Cd_{x}Te mixed crystals for x values up to 0.2 were calculated using tight binding approach. The calculated band gap in the L-point increases with the Cd content in qualitative agreement with photoluminescence measurements in the infrared. For all studied Pb_{1-x}Cd_{x}Te samples, the Hall effect and electrical conductivity measurements, performed in the temperature range from 4 to 300 K, revealed p-type conductivity.
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