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1
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Indirect Coupling Between Localized Magnetic Moments in Zero-Dimensional Graphene Nanostructures (Quantum Dots)

100%
Szałowski K.
Acta Physica Polonica A
|
2014
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vol. 126
|
issue 1
236-237
EN
The indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling between on-site magnetic impurities is studied for two kinds of graphene nanoflakes consisting of approximately 100 carbon atoms, posessing either zigzag or armchair edge. The tight-binding Hamiltonian with Hubbard term is used in non-perturbative calculations of coupling between the impurities, placed at the edge of the structure. In general, for zigzag-edged nanoflakes a pronounced coupling robust against charge doping is found, while for armchair-edged structures the interaction is weaker and much more sensitive to charge doping. Also the distance dependence of indirect exchange differs significantly for both edge forms.
2
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The RKKY Coupling of Two Magnetically Doped Monolayers in Thin Films

63%
Szałowski K., Balcerzak T.
Acta Physica Polonica A
|
2008
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vol. 114
|
issue 5
1375-1382
EN
The Gauss-type exchange contact potential is applied to derive the Ruderman-Kittel-Kasuya-Yosida interaction in thin films. The interlayer magnetic coupling energies and the critical Curie/Néel temperatures are calculated. The quantum size effects are found to cause long-range oscillatory behavior of these quantities vs. film thickness, with the period much longer than the usual RKKY characteristic oscillations.
3
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Ground-State Phase Diagram of a Model FCC Magnet with Modified RKKY Interaction

63%
Szałowski K., Balcerzak T.
Acta Physica Polonica A
|
2008
|
vol. 113
|
issue 1
421-424
EN
The ground-state phase diagram is studied for a diluted model magnet with FCC structure and modified Ruderman-Kittel-Kasuya-Yosida interaction. The modification consists in taking into account the exponential damping for the long-range interaction as well as the nearest-neighbors antiferromagnetic superexchange couplings. The existence of paramagnetic, ordered ferromagnetic and three distinct antiferromagnetic phases is shown. The stability areas of the phases upon the free-carriers concentration are investigated.
4
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Exact Diagonalization Study of an Extended Hubbard Model for a Cubic Cluster at Quarter Filling

45%
Szałowski K., Balcerzak T., Jaščur M., Bobák A., Žukovič M.
Acta Physica Polonica A
|
2017
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vol. 131
|
issue 4
1012-1014
EN
In the paper the thermodynamics of a cubic cluster with 8 sites at quarter filling is characterized by means of exact diagonalization technique. Particular emphasis is put on the behaviour of such response functions as specific heat and magnetic susceptibility. The system is modelled with extended Hubbard model which includes electron hopping between both first and second nearest neighbours as well as Coulombic interactions, both on-site and between nearest-neighbour sites. The importance of hopping between second nearest neighbours and Coulombic interactions between nearest neighbours for the temperature dependences of thermodynamic response functions is analysed. In particular, the predictions of the Schottky model are compared with the calculations based on the full energy spectrum.
5
Content available remote

Ferromagnetic Transition in Ge_{1-x}Mn_{x}Te Layers

27%
Knoff W., Domukhovski V., Dybko K., Dziawa P., Jakieła R., Łusakowska E., Reszka A., Świątek K., Taliashvili B., Story T., Szałowski K., Balcerzak T.
Acta Physica Polonica A
|
2009
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vol. 116
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issue 5
904-906
EN
Ferromagnetic transition temperature in thin layers of diluted magnetic (semimagnetic) semiconductor Ge_{1-x}Mn_{x}Te was studied experimentally by SQUID magnetometry method and analyzed theoretically for a model Ising-type diluted magnetic system with Ruderman-Kittel-Kasuya-Yosida indirect exchange interaction. The key features of the experimentally observed dependence of the Curie temperature on Mn content (x ≤ 0.12) and conducting hole concentration p = (1-10) × 10^{21} cm^{-3} were reproduced theoretically for realistic valence band and crystal lattice parameters of p-Ge_{1-x}Mn_{x}Te taking into account short carrier mean free path encountered in this material and Ruderman-Kittel-Kasuya-Yosida mechanism with both delta-like and diffused character of spatial dependence of the exchange coupling between magnetic ions and free carriers.
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