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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
|
1993
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vol. 84
|
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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Double Exchange in Mixed-Valency Diluted Magnetic Semiconductors

100%
Blinowski J., Kacman P.
Acta Physica Polonica A
|
1996
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vol. 90
|
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.
3
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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.
4
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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.
5
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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
|
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.
6
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Spin-Dependent Interaction of a Band Electron with Paramagnetic Impurities

100%
Blinowski J., Kacman P.
Acta Physica Polonica A
|
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.
7
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Correlations in Magnetic-Nonmagnetic Semiconductor Superlattices - Simple Model

100%
Blinowski J., Kacman P.
Acta Physica Polonica A
|
1997
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vol. 92
|
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.
8
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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.
9
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Ferromagnetism in Cr-Based Diluted Magnetic Semiconductors

81%
Blinowski J., Kacman P., Majewski J.
Acta Physica Polonica A
|
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.
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