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1
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Some Statistical Properties of the Rough Surface

100%
Balcerzak T.
Acta Physica Polonica A
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1993
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vol. 83
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issue 5
597-610
EN
The temperature induced roughening of the solid surface is described by means of a discrete Gaussian model, using integral operator technique. On the basis of the exact statistical identities, the formulae for several local moments, i.e. ⟨hi⟩), ⟨(hi)^{2}⟩ and ⟨hihj⟩ are derived. The results of computer calculations, including surface specific heat, are presented for three lattices with z = 3, 4, and 6. In discussion, some further applications of the presented method are suggested.
2
Content available remote

Magnetic Properties of Thin Film with S = 1

64%
Balcerzak T., Gzik M.
Acta Physica Polonica A
|
1997
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vol. 91
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issue 2
293-296
EN
Blume-Emery-Griffiths model with single-ion anisotropy and biquadratic interactions has been applied for the description of thin magnetic films with S=1. According to the Bogolyubov minimization principle, in the frame of molecular field approximation, the phase diagrams, magnetizations and quadrupolar moments in thin films have been calculated.
3
Content available remote

The RKKY Coupling of Two Magnetically Doped Monolayers in Thin Films

64%
Szałowski K., Balcerzak T.
Acta Physica Polonica A
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2008
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vol. 114
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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.
4
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The Magnetic Specific Heat of the BEG Model

64%
Gzik-Szumiata M., Balcerzak T.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
939-942
EN
The magnetic contribution to the specific heat of the Blume-Emery-Griffiths model with spin-one is studied by the cluster variational method in pair approximation. The nearest neighbour correlation functions are taken into account. The temperature dependencies of the specific heat are calculated and discussed in the context of the phase diagrams obtained recently for the thin film with bilayer geometry.
5
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Magnetic Properties of Thin Film with S=1. Isothermal Susceptibility and Magnetic Specific Heat

64%
Gzik M., Balcerzak T.
Acta Physica Polonica A
|
1997
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vol. 92
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issue 3
543-556
EN
The thermodynamic response functions were studied in thin films in the frame of the Blume-Emery-Griffiths model. The method is based on the analysis of the Gibbs free energy and involves calculations of the magnetization and quadrupolar moment distributions. The temperature dependencies of the susceptibility and specific heat are obtained for various biquadratic interaction parameter and non-zero single-ion anisotropy. The behaviour of these functions in different phases: ferromagnetic, paramagnetic and staggered quadrupolar are illustrated in figures and discussed.
6
Content available remote

Calculations of EuTe Magnetic Phase Diagram for External Pressure

64%
Radomska A., Balcerzak T.
Acta Physica Polonica A
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2000
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vol. 98
|
issue 1-2
83-91
EN
The magnetic phase diagram of europium telluride, EuTe, under external high pressure is theoretically investigated. Besides nearest-neighbour and next-nearest-neighbour exchange interactions, the long-range dipolar and biquadratic interactions are taken into account. The functional dependences of these interactions on the lattice constant are proposed. The calculated Néel and Curie temperatures are compared with the experimental data. Two new phases, antiferrimagnetic and ferrimagnetic, have been found at a high pressure and low temperatures.
7
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Ground-State Phase Diagram of a Model FCC Magnet with Modified RKKY Interaction

64%
Szałowski K., Balcerzak T.
Acta Physica Polonica A
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2008
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vol. 113
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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.
8
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The Phase Diagram of the Second-Type Antiferromagnet

64%
Balcerzak T., Radomska A.
Acta Physica Polonica A
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2000
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vol. 97
|
issue 5
775-778
EN
We investigate theoretically the phase diagrams of the second-type antiferromagnet with the fcc structure. Besides the nearest-neighbour and next-nearest-neighbour exchange interactions, the biquadratic and long-range dipolar terms are taken into account. The results can be useful to discuss the phase diagram of europium telluride under external pressure.
9
Content available remote

Frustration in a Mixed-Spin Ising Model With Multi-Spin Interactions

51%
Jaščur M., Štubňa V., Szalowski K., Balcerzak T.
Acta Physica Polonica A
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2014
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vol. 126
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issue 1
48-49
EN
In this work we investigate a mixed spin-1/2 and spin-1 Ising model on a decorated square lattice. In addition to standard pair interactions between nearest neighbors, we also consider in our calculations three-site four-spin interactions and the effect of single ion anisotropy. Applying the well-known decoration-iteration transformation, we derive a simple relation between the partition function of the model under investigation and the Onsager's partition function for the simple square lattice. With the help of this mapping relation we are able to calculate exact expressions for all relevant physical quantities of the system (for example, the magnetization, internal energy, Gibbs free energy, entropy and specific heat). The most interesting results have been found in the model without pair interactions. In this case, besides the standard ordered and disordered phases, there also appears an interesting phase which is ordered only partially. Analyzing relevant physical quantities of the system, we have found that the partial ordering is closely related to very strong frustrations that lead to non-zero entropy at T=0.
10
Content available remote

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.
|
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.
11
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Theoretical Study of the Frustrated Ising Antiferromagnet on the Honeycomb Lattice

45%
Bobák A., Lučivjanský T., Žukovič M., Borovský M., Balcerzak T.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
636-638
EN
We study effects of the next-next-nearest-neighbour antiferromagnetic (J₃ < 0) interaction on critical properties (or phase diagram) of the frustrated spin-½ J₁-J₂-J₃ Ising antiferromagnet on the honeycomb lattice by using the effective-field theory with correlations. Beside the ground-state energy, we find that there is a region of J₃ < 0 in which the frustrated honeycomb lattice antiferromagnet exhibits a tricritical point, at which the phase transition changes from the second order to the first one on the line between Néel antiferromagnetic and paramagnetic phases.
12
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
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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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