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  1. 55 Acta Physica Polonica A

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  1. 10 Kamieniarz G.

  2. 5 Dekeyser R.

  3. 5 Esposito F.

  4. 5 Musiał G.

  5. 4 Dębski L.

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1
Content available remote

Site Percolation Thresholds of FCC Lattice

100%
Gawron T., Cieplak M.
Acta Physica Polonica A
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1991
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vol. 80
|
issue 3
461-464
EN
Percolation thresholds, p_{c}, for site diluted spin systems on the fcc lattice are determined for exchange interactions extending up to the shell of the fourth nearest neighbors. If the interactions include the nearest, second, third, and fourth neighbors, p_{c} is equal to 0.198, 0.136, 0.061, and 0.05 respectively. These results agree with the Roberts approximate formula for p_{c}. Estimation of p_{c} to even longer-ranged couplings is presented. For instance for p_{c} = 0.01 the range of the couplings should extend at least to the eight shell of neighbors.
2
Content available remote

Modeling of the Experimental Molecular-Based Ring-Shaped Nanomagnets

100%
Antkowiak M., Kozłowski P., Musiał G., Florek W., Kamieniarz G., Esposito F.
|
|
issue 5
965-966
EN
Quantum transfer matrix technique and numerically exact diagonalization method are applied to the Heisenberg spin systems to model ring-shaped molecules. Two cases are investigated: (i) a dozen of S = 1 spins with additional biquadratic exchange and (ii) a dimetallic molecule Cr_7Cd, where it is assumed that exchange anisotropy is determined in a local coordination system. In the latter case the calculated susceptibility is compared with experimental results.
3
Content available remote

Verification of a New Quantum Simulation Approach through Its Application to Heisenberg-Like Models

100%
Liu Z., Ian H.
Acta Physica Polonica A
|
2016
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vol. 129
|
issue 6
1210-1213
EN
A quantum simulation approach facilitated by the self-consistent algorithm was applied in the present work to ferromagnetic and antiferromagnetic three-dimensional Heisenberg lattices consisting of S = 1 spins. Consequently, the calculated spontaneous magnetizations for the two sorts of lattices are precisely consistent with mean-field theory in the whole temperature range. Especially, the numerical results, such as magnetizations, total energies and total free energies per mole of spins, show no size effects. Thus, the physical properties of a huge bulk magnet can be estimated by performing simulation for a very tiny sample, so that the computational time can be greatly saved.
4
Content available remote

Exchange Coupling and Exchange Bias in FM/AFM Bilayers for a Fully Compensated AFM Interface

80%
Skubic B., Hellsvik J., Nordström L., Eriksson O.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
25-29
EN
We address the interlayer coupling in a ferromagnet/antiferromagnet bilayer where the interface of the antiferromagnet is fully compensated. We discuss the role of different types of exchange interaction for the interlayer coupling and exchange bias. We propose two types of corrections to the ideal Heisenberg Hamiltonian which may explain exchange bias. The first is a correction for the angular dependence of the exchange interactions and the second a correction due to magnetostriction and interface imperfections. The first correction contributes to an anisotropy at the interface and favors either parallel or perpendicular coupling across the interface. The second correction contributes to the exchange bias. Our analysis is based on atomic spin dynamics simulations, and our results show that small corrections to the ideal Heisenberg Hamiltonian may have macroscopic consequences in systems with frustrated interatomic interactions.
5
Content available remote

Arbitrarily Weak First Order Phase Transitions in the 3D Standard Ashkin-Teller Model by MC Computer Experiments

80%
Jeziorek-Knioła D., Musiał G., Wojtkowiak Z.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
327-329
EN
The first order phase transition line in the vicinity of the tricritical Ising point region is studied in the 3D standard Ashkin-Teller model on a cubic lattice. The large-scale Monte Carlo computer experiments using the Binder- and Challa-like cumulants, the latter modified by Musial, are proposed and performed. Specific behavior of the Challa-Musial cumulants for weak first order phase transitions is discovered and its interpretation is proposed. The paper proves the arbitrarily weak first order character of phase transitions when approaching to the Ising point.
6
Content available remote

Magnetic Structures in Ultrathin Films and Nanostructures: Simulation

80%
Lévy J., Ghazali A., Vedmedenko E.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
431-434
EN
In magnetic ultrathin films and dots, competing exchange, anisotropy and dipolar couplings lead to a large variety of magnetic structures. These structures are obtained by means of the Monte Carlo simulations. Three classes of magnetic structures are obtained according to anisotropy-to-dipolar energy ratio: Ising striped structures, XY-spin structures with vortices, and twisted spin phases at the spin = reorientation transition. Domain wall nucleation and motion at the coercive field are also accessible.
7
Content available remote

Computation of Latent Heat based on the Energy Distribution Histogram in the 3D Ashkin-Teller Model

80%
Jeziorek-Knioła D., Wojtkowiak Z., Musiał G.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
435-437
EN
The method of computation of the latent heat based on the energy distribution histogram is applied to the standard 3D Ashkin-Teller (AT) model. Similarly as in the original method for the q-state Potts model for strong first order phase transitions, the characteristic histogram with two peaks in the critical region have been observed. Positions of two minima of negative logarithm of internal energy probability for samples of finite size show good linear scalability to the thermodynamic limit. The applicability of this method has been confirmed by proving that the latent heat values are consistent with the ones obtained by us using the analysis of the behavior of the cumulants of the type of Challa and of Lee-Kosterlitz. The presented method is far more efficient than the one based on those cumulants.
8
Content available remote

d-Wave Superconductivity, Orbital Magnetism, and Unidirectional Charge Order in the t-J Model

80%
Raczkowski M.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
107-114
EN
Recent scanning tunneling microscopy in the superconducting regime of two different cuprate families revealed unidirectional bond-centered modulation in the local electronic density of states. Motivated by this result we investigate the emergence of modulated d-wave superconductivity coexisting with charge domains that form along one of the crystal axes. While detailed stripe profiles depend on the used form of the Gutzwiller factors, the tendency towards a valence bond crystal remains robust. We also find closely related stripe phase originating from the staggered flux phase, a candidate for the pseudogap phase of lightly doped cuprates.
9
Content available remote

Numerical Test of Molecular-Field Renormalization Group

80%
Kamieniarz G.
Acta Physica Polonica A
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1997
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vol. 92
|
issue 2
423-426
EN
A new transfer matrix approach has been worked out to test the predictions of the molecular-field renormalization group for square Ising clusters with a linear size up to L ≤ 11. The convergence of the finite-size critical couplings towards the exact value for the molecular-field renormalization group is shown and the limit of the ratio y_{h}/y_{t} consistent with the corresponding universal value is revealed.
10
Content available remote

2D Falicov-Kimball Model in the Perturbative Regime at Finite Temperatures

80%
Dębski L.
Acta Physica Polonica A
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2009
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vol. 115
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issue 1
156-158
EN
Finite-temperature properties of the Falicov-Kimball model in two approximations were studied in the perturbative regime, i.e. for t/U ≪ 1, where t=1 is the hopping constant and U=10 denotes the Coulomb interaction strength. In our study, we determined the phase diagram of the model in the second order of the perturbation theory, where it reduces to the antiferromagnetic Ising model in the emergent magnetic field. In the fourth order, where our model constitutes the Ising model with more complicated frustrated antiferromagnetic interactions, the phase diagram was established. The Monte Carlo method was employed to investigate the phase transition lines. The existence of stripe ordering at finite temperatures is proved.
11
Content available remote

Effect of the Sign of Anisotropy Constants on the Properties of the System of Interacting Ferromagnetic Nanoparticles

80%
Sadek M., Marchwiany M., Woinska M., Majhofer A., Gosk J., Twardowski A., Szczytko J.
Acta Physica Polonica A
|
2016
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vol. 129
|
issue 1a
A-53-A-55
EN
We use the Monte Carlo simulation method to investigate the influence of the signs of magnetocrystalline anisotropy constants and the magnetic dipole-dipole interactions on the zero field cooled-field cooled magnetization experiments and hysteresis curves of a system of magnetic nanoparticles. Positive first cubic anisotropy constant K₁ results in larger blocking temperatures and larger coercive fields of a system, while the second anisotropy constant K₂ is practically of negligible importance for the phenomena investigated. Magnetic dipole-dipole interactions are important only in the most dense systems of particles and their effects practically disappear for systems where the distance between the closest particles exceeds three particle diameters.
12
Content available remote

Magnetic Properties of Multilayer Thin Film with Ising-Like Ordering

80%
Bîrsan E.
|
|
issue 3
500-505
EN
In the last years, the study of the antiferromagnetic-ferromagnetic interfaces was a very exciting topic in the thin film area. Using the Monte Carlo technique (by applying the standard Metropolis algorithm) and the extended Heisenberg model with low dipolar interaction, the influence of the antiferromagnetic base layer on the magnetic properties of the multilayer thin film is investigated, in the ferromagnetic region of the phase diagram of the system. For each ferromagnetic layer individually, we study the physical quantities of interest (assuming particular physical conditions): the out-of-plane magnetization, the magnetic susceptibility and the specific heat and we point out the Ising-like ordering of the magnetic spins. The obtained numerical results show that the critical temperature of the individual layers decreases as we approach the base antiferromagnetic layer and consequently, the stability of the ferromagnetic phase increases with the distance from the base layer.
13
Content available remote

Numerical Simulations of Linear S=1 Ferro- and Antiferromagnets

80%
Kamieniarz G., Matysiak R., Caramico D'Auria A., Esposito F., Esposito U.
Acta Physica Polonica A
|
1997
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vol. 92
|
issue 2
387-389
EN
The finite-temperature static properties of the spin S=1 antiferromagnetic Heisenberg chains are extensively simulated using the quantum transfer matrix method. The zero-field susceptibility and specific heat as well as the field-dependent magnetization data are evaluated to select the microscopic parameters of a number of real quasi-one-dimensional compounds and to verify some theoretical approaches.
14
Content available remote

Modeling the Hysteresis Loop of the Nanocomposite Material Using Modified Hyperbolic T(x) Model

80%
Dośpiał M.
Acta Physica Polonica A
|
2015
|
vol. 127
|
issue 2
415-417
EN
The paper presents possibilities of hysteresis loop decomposition onto the magnetization components. The reversible and irreversible magnetization changes describe processes, which are influencing reversal magnetization in studied permanent magnets. Further, these components are used for modelling the recoil curves using modified hyperbolic T(x) model.
15
Content available remote

Modelling Hysteresis Loops in Fe-Based Soft Magnetic Composites Using Takács Description

80%
Jankowski B., Ślusarek B., Szczygłowski J., Chwastek K.
Acta Physica Polonica A
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2015
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vol. 128
|
issue 1
116-119
EN
The measurements and modeling of hysteresis loops of soft magnetic composites made of powder with different particle sizes and different densities were investigated. The Takács description that is based on hyperbolic tangent transformation has been applied in the consideration. The paper shows recorded hysteresis loops with the maximum flux density of 1.2 T.
16
Publication available in full text mode
Content available

Simulation of Unsaturation Domain Formation in Antiferromagnetic Multilayers

80%
Major M., Bottyán L., Nagy D.
Acta Physica Polonica A
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2002
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vol. 101
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issue 2
301-305
EN
A two-dimensional phenomenological model of patch-domain formation on unsaturation in strongly coupled tri- and multilayer antiferromagnets is presented. Domain patterns are simulated using a fast Monte Carlo algorithm. As a first example the autocorrelation function of the simulated domain pattern is compared with that of a measured Kerr image.
17
Content available remote

Monte Carlo Simulations of Ferromagnetic Nanocomposites

80%
Woińska M., Majhofer A., Gosk J., Szczytko J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1019-1021
EN
We present results of Monte Carlo simulations of a model system of Co nanoparticles in an external magnetic field. In our simulations we take into account the interaction with the external magnetic field, the energy of crystallographic anisotropy and the dipole-dipole interactions between single domain nanoparticles. We apply the standard Metropolis algorithm to a cluster of 27 randomly distributed superparamagnetic Co nanoparticles. We investigate the dependence of blocking temperature T_{B} on particle and cluster size.
18
Publication available in full text mode
Content available

Effect of Surface Anisotropy in Core-Shell Bimetallic Nanoparticles

80%
Tornau E., Petrauskas V., Crisan O.
Acta Physica Polonica A
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2005
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vol. 107
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issue 2
425-428
EN
Temperature dependences of magnetization of core-shell-type nanoparticles with non-magnetic core and ferromagnetic shell are obtained using Monte Carlo simulation. The influence of surface spin disorder of the ferromagnetic shell on overall shape of magnetization curve is analyzed. The magnetic state diagram (in shell thickness - surface anisotropy coordinates), separating collinear and non-collinear states, is determined.
19
Content available remote

Spinodal Decomposition of Magnetic Ions in Eu-Codoped Ge_{1-x}Cr_{x}Te

80%
Podgórni A., Kilanski L., Dobrowolski W., Górska M., Reszka A., Domukhovski V., Kowalski B., Brodowska B., Anderson J., Butch N., Slynko V., Slynko E.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1012-1015
EN
We present the experimental evidence for the presence of spinodal decomposition of the magnetic ions in the Ge_{1-x-y}Cr_{x}Eu_{y}Te samples with chemical composition varying in the range of 0.015 ≤ x ≤ 0.057 and 0.003 ≤ y ≤ 0.042. The ferromagnetic transition at temperatures 50 ≤ T ≤ 57 K was observed, independent of the chemical composition. The long-range carrier mediated itinerant magnetic interactions seem to be responsible for the observed ferromagnetic order. The magnetic irreversibility with coercive field H_C = 5 - 63 mT and the saturation magnetization M_S ≈ 2 - 6 emu/g are found to strongly depend on the chemical composition of the alloy.
20
Content available remote

Improved Phase Diagrams of Ashkin-Teller Model

80%
Pawlicki P., Kamieniarz G., Kozlowski P., Dekeyser R., Rogiers J.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
453-458
EN
The phase diagram of the Askhin-Teller model in two dimensions is determined. Numerical calculations are performed for the simple square L × L lattice using transfer matrix technique. Exploiting finite-size scaling all unknown critical lines were obtained with good accuracy. An extended version of the Ashkin-Teller model is also considered within the molecular field renormalization group method and the critical surface for three-parameter odd-parity Hamiltonian is calculated.
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