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  1. 35 Acta Physica Polonica A

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  1. 4 Akin H.

  2. 4 Kamieniarz G.

  3. 3 Ganikhodjaev N.

  4. 3 Temir S.

  5. 3 Uguz S.

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1
Publication available in full text mode
Content available

Embedded Atom Method for Theoretical Strength and Stability of Some fcc Metals

100%
Öztekin Çiftci Y., Çolakoğlu K.
Acta Physica Polonica A
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2001
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vol. 100
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issue 4
539-551
EN
The structural phase transformation and theoretical strength of fcc metals Ni, Cu, Ag, Al, Au, and Pt under [100] uniaxial loading are studied by using analytical embedded-atom-potential method. In the present calculations the stress-free bcc phase is found unstable and fcc phase is found to be stable. The obtained energy differences of fcc-bcc phases are comparable with those found by the first-principles calculations and experiments for all metals considered. The present pair potential in the embedded-atom method is used for the first time for this purpose. Theoretical lattice parameters, volumes, and energies of the bcc and fcc structures for each metal at zero pressure are calculated and compared with the available experimental values. Third-order elastic constants and pressure-volume curves for studied metals are also investigated and found generally good agreement with experiments.
2
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Phase Transition in Quasi-Two-Dimensional Horizontally Driven Granular System

100%
Shah S., Li Y., Khan W., Din N., Chand R.
Acta Physica Polonica A
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2012
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vol. 121
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issue 3
699-702
EN
In an experimental setup, consisting of quasi-two-dimensional square cell, the motion of monodisperse spherical steel balls is studied. The cell is vibrated horizontally to eradicate the compaction of balls due to gravity. By raising the number density of the steel balls, the dilute fluid has been gradually alternated into dense fluid. The temperature of granular media, along the driven and transverse directions, has been found to be anisotropic. Transition from granular gas to the liquid-like fluid has been observed. The radial distribution function of the balls in the cell is investigated for the authentication of the structural changes. Furthermore, the fast Fourier transformation for the 2D system is carried out to confirm these changes.
3
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Electromagnetic Waves Generation in Ni_{2.14}Mn_{0.81}GaFe_{0.05} Heusler Alloy at Structural Phase Transition

100%
Bychkov I., Kuzmin D., Kalenov D., Kamantsev A., Koledov V., Kuchin D., Shavrov V.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
588-590
EN
Electromagnetic waves generated by the Heusler alloy Ni_{2.14}Mn_{0.81}GaFe_{0.05} at structural phase transition was detected in the frequency range of 28-32 GHz. Influence of the kinetics of phase transitions on the nature of the sample millimeter radiation was studied as well. It has been observed that the contribution of the intrinsic radiation increases with increasing of the heating/cooling rate. The possible mechanisms and theory of such effect is discussed. It is shown that the maximum radiation intensity should be emitted in direction perpendicular to the movement of interphase boundary.
4
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Applications of Density Matrix Renormalization Group to Problems in Magnetism

100%
Gehring G. A., Bursill R. J., Xiang T.
Acta Physica Polonica A
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1997
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vol. 91
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issue 1
105-119
EN
The application of real space renormalization group methods to quantum lattice models has become a topic of great interest following the development of the density matrix renormalization group by White. This method has been used to find the ground and low-lying excited state energies and wave functions of quantum spin models in which the form of the ground state is not clear, for instance because the interactions are frustrated. It has also been applied to fermion problems where the tendency for localization due to the strong Coulomb repulsion is opposed by the lowering of the kinetic energy which occurs as a result of electron transfer. The approach is particularly suitable for one-, or quasi-one-dimensional problems. The method involves truncating the Hilbert space in a systematic and optimised manner. Results for the ground state energy are thus variational bounds. The results for low-lying energies and correlation functions for one-dimensional systems have unprecedented accuracy and the method has become the method of choice for solving one-dimensional quantum spin problems. We review the method and results obtained for the spin-1 chain with biquadratic exchange as well as the spin-1/2 model with competing nearest and next nearest neighbour exchange will be described. More recently, the density matrix renormalization group has been applied to reformulate the coupling constant renormalization group approach which is appropriate for the study of critical properties. This approach has been applied to the anisotropic spin-1/2 Heisenberg chain. Finally, we discuss recent work which has borne promising applications in two dimensions - the Ising model and the two-dimensional Hubbard model.
5
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On Melting of Two-Dimensional Monolayer Films

100%
Patrykiejew A., Zientarski T., Binder K.
Acta Physica Polonica A
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1996
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vol. 89
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issue 5-6
735-742
EN
The melting of two-dimensional films formed on the (100) fcc crystal is studied by Monte Carlo simulation. The results obtained suggest that in systems with only weakly corrugated surface potential, exhibiting the hexagonal close packed solid structure, the melting transition is followed by the Ising-type transition as predicted by the theory of Nelson and Halperin. In the case of highly corrugated surface potential, the film forms registered structure which disorders gradually as the temperature is raised.
6
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Temperature and Pressure Dependence of the Linewidth for an Internal Mode in the Solid Phases of Benzene

100%
Yurtseven H., Şenol M.
Acta Physica Polonica A
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2013
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vol. 124
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issue 4
698-701
EN
The pressure dependence of the Raman linewidths for the ν_1 breathing mode is analyzed using the experimental data from the literature for the solid phases (I, II, III and III') in benzene. Increase (I, III and III') and decrease (II) in the Raman linewidths are described by a power-law analysis with the critical exponent β. The β values we find, which characterize the phase transition are in favour of the first order among those phases considered in benzene. The temperature and pressure dependence of the frequencies and linewidths of various Raman modes can be analyzed using a power-law formula, as studied here for the solid phases (I, II, III and III') in benzene when the experimental data are available in the literature.
7
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EPR Study of Monoclinic RbD_{2}PO_{4} Monocrystal Doped with Cr^{5+} Ion

100%
Waplak S., Shuvalov L.
Acta Physica Polonica A
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1995
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vol. 87
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issue 3
643-648
EN
Deuterated monoclinic RbD_{2}PO_{4} (DRDP) doped with chromium Cr^{5+} is studied by EPR in 90 K to 400 K temperature range. EPR reveals two types of paramagnetic centers: single Cr^{5+} (S = 1/2) complex and Cr^{5+}-Cr^{5+} coupled pairs with effective spin S = 1. The EPR line splitting of single Cr^{5+} complex in DRDP versus temperature agrees with the unit cell multiplica­tion. The splitting of EPR line of pair spectrum appears at T* = 160 K, far below the phase transition temperatures and is due to the anisotropy of the exchange interaction. The clustering effect in the low-dimensional DRDP is suggested.
8
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Rayleigh Scattering of Mössbauer Radiation Method Used in Dynamics Studies of Condensed Matter

80%
Enescu S., Bibicu I.
Acta Physica Polonica A
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2005
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vol. 107
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issue 3
479-489
EN
The Rayleigh scatte ring of the Mössbauer radiation is a less common technique used in the study of the properties of condensed matter. The detection of the scattered radiation via the nuclear resonance absorption, with an energy resolution of the order of 10^{-8} eV makes this technique very sensitive to dynamics changes. The results of our studies by the Rayleigh scattering of the Mössbauer radiation on pyrolytic graphite (C) and rubidium tetrachlorozincate (Rb_2ZnCl_4) are reported. The contribution of the coherent inelastic scattering to the total intensity in C(002) is presented like a consequence of the coupling motions of C atoms in the hexagonal plane. The normal-incommensurate phase transition in Rb_2ZnCl_4 is discussed in connection with the photon-phonon interaction.
9
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Stripe Phases in the Hubbard Model

80%
Góra D., Rościszewski K., Oleś A.
Acta Physica Polonica A
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2000
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vol. 97
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issue 1
225-228
EN
We investigate the magnetic and charge ordering in the stripe phases obtained while using correlated wave functions for finite 8×8 clusters described by the Hubbard model with extended hopping. Nonmagnetic vertical (01) site-centered domain walls and (11) bond-centered stripes are found for the parameters of La_{2-x}Sr_{x}CuO_{4} and YBa_{2}Cu_{3}O_{6+x}, respectively, at doping δ=1/8. The obtained half-filled domain nonmagnetic walls reproduce the maxima observed in neutron scattering for La_{2-x}Sr_{x}CuO_{4}.
10
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On Gibbs Measures of the Potts Model with Three Competing Interactions on Cayley Tree of Order 3

80%
Akin H., Saygılı H.
Acta Physica Polonica A
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2016
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vol. 129
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issue 4
845-848
EN
In this paper, we consider the Potts model with competing interactions on the Cayley tree of order three. We give the Potts model on the Cayley tree and its recursion relation. We construct the Gibbs states corresponding to the model by using Markov random field method. We calculate the critical curve, such that there is a phase transition for the model. We show that there are phase transition of the model for some given parameters. We extend the results obtained by Akin and Temir (Condensed Matt. Phys. 14, 23003 (2011)).
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The Magnetic Equation of State and Transport Properties in Reduced Dimensions

80%
Warda K., Wojtczak L.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
878-880
EN
Basing our considerations on magnetic equation of state applied to the description of magnetic systems of confined geometry we developed the model of calculations of the electrical resistivity for metallic multilayers. It was shown that in the transport of charge in ferromagnetic material d-electrons play an important role. The key parameters in the presented model are: the width of the electron energy band and the shift of the energy level for two spin orientations as well as the Fermi energy and size of the sample (the thickness of magnetic and nonmagnetic layers and the total number of layers). The presented results of calculations for temperature dependence of magnetoresistance are in qualitative agreement with the available experimental data. The model calculations introduced in this paper can be applied to current-in-plane geometry as well as to current-perpendicular-to-plane geometry. The calculations are valid within the limitations of the resistor network model.
12
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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
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1997
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vol. 92
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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.
13
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Growth Dynamics of Photoinduced Phase Domain in Cyano-Complex Studied by Boundary Sensitive Raman Spectroscopy

80%
Asahara A., Nakajima M., Fukaya R., Tokoro H., Ohkoshi S., Suemoto T.
Acta Physica Polonica A
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2012
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vol. 121
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issue 2
375-384
EN
Rubidium manganese hexacyanoferrate exhibits charge transfer phase transition from high temperature phase to low temperature phase at 230 K. This phase transition can also be triggered by light irradiation resonantly inducing charge transfer from Mn^{2+} to Fe^{3+}. In the present study, boundary sensitive Raman spectroscopy was performed for Rb_{0.94}Mn[Fe(CN)_6]_{0.98}·0.2H_2O in both cases of photoinduced and thermal phase transition. Since the frequencies of C ≡ N stretching vibration modes are very sensitive to the valence states of the adjacent metal ions, we can quantify the distribution of not only high and low temperature phase but also boundary configurations from the observed spectra. We obtained the time evolution of the fraction ratios of the valence states from the observed peak areas. In the case of photoinduced situation, the boundary increases up to 15% when high temperature phase diminishes to 55% of the initial fraction. This is quite different from the result in thermal phase transition where the boundary is created only 0.8% at the same high temperature phase fraction value. We conclude that many small domains are preferably created in photoinduced phase transition since the ratio of boundary is large, while large domains grow in thermal phase transition.
14
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Content available

Spin Reorientation Studies in Nd_2Fe_{14-x}Si_xB (0

80%
Gargula R., Pędziwiatr A., Bogacz B., Wróbel S., Bartolomé J., Stankiewicz J.
Acta Physica Polonica A
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2002
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vol. 101
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issue 2
289-294
EN
Nd_2Fe_{14-x}Si_xB (x=0.25, 0.5, 0.75, 1.0, 1.5, 2.0) intermetallic compounds were investigated by magnetometry, ^{57}Fe Mössbauer effect, electric resistivity, and differential scanning calorimetry mainly in the vicinity of the spin reorientation temperature, T_{SR}. The Curie temperature, T_C, and T_{SR} were determined for different compositions and the spin phase diagram was constructed. ^{57}Fe Mössbauer spectra showed noticeable changes in the reorientation region. For temperatures above the transition, the spectra were analysed using 6 Zeeman patterns associated with 6 inequivalent crystal sites in Nd_2Fe_{14}B according to site occupations (16k_1:16k_2:8j_1:8j_2:4c:4e). In the transition region, 12 subspectra had to be incorporated in the analysis. Electric resistivity measurements showed a typical metallic behaviour with no anomalies in the magnetic transition region. Differential scanning calorimetry measurements revealed broad endothermic two stage peaks around T_{SR}.
15
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Excitonic Instabilities of Deformable Lattice - from Self-Trapping to Phase Transition

80%
Toyozawa Y.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
47-56
EN
The optically created exciton will be self-trapped if its coupling to phonons is strong enough, and will moreover be self-decomposed if the elec­tron and the hole couple to phonons in an opposite way. The bistability between the parity-conserved and parity-broken self-trapped excitons was observed in alkali halides. The situation is most dramatic if the bistability between the parity-broken self-trapped exciton and the ground state (with no exciton) comes into play since the electron-hole pairs may then be sponta­neously generated at every lattice site, resulting in the electronic and struc­tural phase transition. The neutral to ionic phase transition observed in a few organic charge transfer compounds under applied pressure or decreasing tem­perature can be considered as an example. Recent experiment revealed that TTF-chloranil, among others, is subject to photo-induced transient phase change over hundreds of unit cells per one photon. The dynamics of this process can be described in terms of self-trapping and self-multiplication of a photo-generated charge transfer exciton along the chain through the at­tractive dipolar interaction. This description of phase transition in terms of exciton dynamics will provide a new paradigm of materiology.
16
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Earth Materials at High Pressure and Temperature: Recent Contributions from in situ Synchrotron X-Ray Diffraction

80%
Redfern S. A. T.
Acta Physica Polonica A
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1997
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vol. 91
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issue 4
659-668
EN
The application of synchrotron X-ray powder diffraction to the study of minerals and understanding of the structure and dynamics of the Earth's deep interior is summarised. The salient features of the diamond anvil cell and large-volume multi-anvil cell high-P/T apparatus as used at synchrotron radiation sources are described, and recent developments and applications of these techniques within high-P/T mineralogy are reviewed.
17
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Magnetic Phases and Generalized t-J Models in Doped Mott-Hubbard Insulators

80%
Oleś A., Zaanen J.
Acta Physica Polonica A
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1994
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vol. 85
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issue 1
145-163
EN
We review some recent results obtained for the dynamics of a single hole and for the ground states at finite hole doping in t-J model. Next, we address the role of orbital degeneracy in doped Mott-Hubbard insulators and show examples of effective strong coupling models which include the orbital degrees of freedom. These new t-J models have interesting phase diagrams, with the new magnetic phases stabilized by a competition between magnetic energy and excitonic excitations. It is argued that the doped holes always bind to the excitons and that the new phases identified on the mean-field level give rise to local distortions of the lattice. We conclude that realistic t-J models derived from the electronic structure of particular compounds may be successfully applied for understanding both the observed magnetic ground states, and the results of photoemission experiments, as we have demonstrated recently for NiO.
18
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Magnetic Properties of Thin Film with S=1. Isothermal Susceptibility and Magnetic Specific Heat

80%
Gzik M., Balcerzak T.
Acta Physica Polonica A
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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.
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Quantum Effects and Critical Behavior in Low-Dimensional Spin-1/2 Systems

80%
Kamieniarz G., Musial G., Dębski L., Bieliński M., Dekeyser R.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
445-447
EN
The critical coupling and spontaneous magnetization curve for the 2D-Ising model are calculated using the effective-field method with correlations. An application of the method to the quantum S=1/2 1D-Heisenberg model is presented and reliable low-temperature estimates of the specific heat are evaluated.
20
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Asymmetry Driven Phase Transformations

80%
Damczyk J., Ostasiewicz K., Radosiński Ł., Radosz A.
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issue 4
527-530
EN
Motivated by the properties of one-dimensional lattice systems with asymmetric on-site potential, one can formulate a hypothesis of an asymmetry driven phase transformation. Characteristic feature of one-dimensional systems exhibiting asymmetry driven phase transformation is a sequence of the two phase conversions. In particular class of such systems with a triple-well potential, phase conversions of one-dimensional systems would evolve into a sequence of two phase transitions in three-dimensional models. We propose here a model of three-dimensional system exhibiting a sequence of two first order asymmetry driven phase transitions.
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