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1
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Monte Carlo Study of a Spin-3/2 Blume-Emery-Griffiths Model on a Honeycomb Lattice

100%
Žukovič M., Jaščur M.
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vol. 126
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issue 1
36-37
EN
We study the phase diagram of the spin-3/2 Blume-Emery-Griffiths model on a honeycomb lattice by Monte Carlo simulations in order to verify the presence of some peculiar features predicted by the effective field theory (EFT) with correlations. The locations of the order-disorder phase boundaries are estimated from thermal variations of the magnetic susceptibility curves. It is found that for positive values of the biquadratic interactions the critical boundary shows a discontinuous character as a function of the single-ion anisotropy strength, in line with the EFT expectations. However, for negative values of the biquadratic interactions the step-like variation of the critical frontier predicted by EFT was not reproduced.
2
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Frustration in a Mixed-Spin Ising Model With Multi-Spin Interactions

81%
Jaščur M., Štubňa V., Szalowski K., Balcerzak T.
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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.
3
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Reentrant Transitions of Ising-Heisenberg Ferromagnet on a Triangular Lattice with Diamond-Like Decorations

81%
Jaščur M., Strečka J., Čanová L.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
453-456
EN
The mixed spin-1/2 and spin-1 Ising-Heisenberg ferromagnet on the decorated triangular lattice consisting of inter-connected diamonds is investigated within the framework of an exact decoration-iteration mapping transformation. It is shown that the diamond-like decoration by a couple of the Heisenberg spins gives rise to a diverse critical behaviour including reentrant phase transitions with two consecutive critical points.
4
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Ground-State Phase Diagram of Geometrically Frustrated Ising-Heisenberg Model on Doubly Decorated Planar Lattices

81%
Čanová L., Strečka J., Dely J., Jaščur M.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
449-452
EN
Ground-state phase diagram of the mixed spin-1/2 and spin-1 Ising-Heisenberg model on doubly decorated planar lattices is examined using the generalized decoration-iteration transformation. The main attention is devoted to the comparison of the ground-state properties of the quantum Ising-Heisenberg model and its semi-classical Ising analogue.
5
Content available remote

Spin-1/2 XXZ Diamond Chain within the Jordan-Wigner Fermionization Approach

81%
Verkholyak T., Strečka J., Jaščur M., Richter J.
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issue 5
978-979
EN
The spin-1/2 XXZ diamond chain is considered within the Jordan-Wigner fermionization. The fermionized Hamiltonian contains the interacting terms which are treated within the Hartree-Fock approximation. We obtain the ground-state magnetization curve of the model for some particular cases and compare the results with the exact diagonalization data for finite chains of 30 spins and known exact results. We also analyze the validity of the suggested approximation.
6
Content available remote

Exact Diagonalization Study of an Extended Hubbard Model for a Cubic Cluster at Quarter Filling

71%
Szałowski K., Balcerzak T., Jaščur M., Bobák A., Žukovič M.
Acta Physica Polonica A
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2017
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vol. 131
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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.
7
Content available remote

KEr(MoO_{4})_{2} and CsDy(MoO_{4})_{2} - Low-Dimensional Ising Magnets

52%
Kačmár M., Orendáčová A., Čizmár E., Horváth D., Orendáč M., Bondarenko V., Anders A., Feher A., Jaščur M.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
807-810
EN
In the present work the behaviour of cluster excitations in magnetic field, B, parallel to the easy axis was experimentally studied by the measurements of KEr(MoO_{4})_{2} and CsDy(MoO_{4})_{2} specific heat, C, vs. B dependence studied at a constant temperature. Corresponding Monte Carlo simulations of C revealed that despite of the fact that the Ising exchange-coupling models proved useful for a sufficient description of the specific heat of these dipolar systems in B=0, the analysis of current experimental data requires a partial renormalization of exchange-coupling constants previously obtained from B=0 analysis. The influence of crystal field effects and long-range character of spin correlations is discussed.
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