Search results

1

The Spin-1/2 Ising Model on the Bow-Tie Lattice as an Exactly Soluble Free-Fermion Model

100%

Strečka J., Čanová L.

Acta Physica Polonica A

|

2008

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vol. 113

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issue 1

457-460

EN

The spin-1/2 Ising model on the bow-tie lattice is exactly solved by establishing a precise mapping relationship with its corresponding free-fermion eight-vertex model. Ground-state and finite-temperature phase diagrams are obtained for the anisotropic bow-tie lattice with three different exchange interactions along three different spatial directions.

2

Reentrant Transitions of Ising-Heisenberg Ferromagnet on a Triangular Lattice with Diamond-Like Decorations

100%

Jaščur M., Strečka J., Čanová L.

Acta Physica Polonica A

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2008

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vol. 113

|

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.

3

Composition and Order-Disorder Transition in the Cu_3Au (001) Surface Layer Investigated with the Use of DAES and DEPES

100%

Rok Ł., Mróz S.

Acta Physica Polonica A

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2008

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vol. 114

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issue S

S-115-S-124

EN

The composition of the first atomic layer of Cu_3Au(001) crystal (about half-and-half copper and gold atoms) changes only slowly even at temperatures much higher than that of the order-disorder transition (T_C = 663 K). Theoretical and experimental works show a general trend of these changes but they differ in quantitative findings. In the present work we used directional elastic peak electron spectroscopy and directional Auger electron spectroscopy to investigate changes of atomic order and composition in the first atomic layers of the Cu_3Au(001) crystal during the sample temperature increase. The height of central maximum in DEPES polar profile of the sample investigated was measured as a function of sample temperature. It was found that the measured dependence is linear, but the slope of this dependence changes abruptly around T_C. This change seems to be connected with disappearance of the atomic order in the first and second atomic layers. In DAES the height of the Auger peaks for copper and gold low energy transitions (MVV and NVV, respectively) were measured in the dN(E)/dE mode as a function of the primary electron beam incidence angle. The composition of the first, second, and third atomic layers was determined by fitting the ratio of calculated DAES polar profiles for copper and gold to such a ratio for the measured profiles.

4

Directional Auger Electron Spectroscopy - Possibilities, Limitations and Proposal of Improvements

100%

Mróz S., Rok Ł.

Acta Physica Polonica A

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2008

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vol. 114

|

issue S

S-93-S-101

EN

Physical foundations of directional auger electron spectroscopy (DAES) and calculation of DAES profiles in single scattering cluster approach are presented. Limitations of this method (application only to investigation of the crystalline structure of homogeneous samples) is shown and explained as the result of participation of inelastically scattered electrons in the Auger signal generation. To extend the DAES application for the interface structure, the use of as low as possible energy of primary electrons is proposed because in such a case the participation of inelastically scattered electrons becomes negligible and single scattering cluster calculation should describe correctly the DAES profiles for interfaces. Besides, the extension of single scattering cluster calculations to the second elastic scattering is recommended. To check the technical possibility of DAES use in the proposed version, the Auger spectrum of Cu LMM peaks was recorded for a Cu_3Au(001) sample with the use of a retarding field analyzer with the primary beam energy 1200 eV. Quality of this spectrum seems to be good enough for using in DAES.

5

Short-Range Order Fluctuation in the Isotropic Phase of Solutions of 4-trans-4'-n-dodecylcyanobiphenyl in Benzene Studied by Nonlinear Dielectric Spectroscopy

80%

Kędziora P.

Acta Physica Polonica A

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2005

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vol. 107

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issue 6

907-916

EN

Nonlinear dielectric spectroscopy is used to study the dynamics of the smectogenic compound 4-trans-4'-n-dodecylcyanobiphenyl in the isotropic phase as a function of its concentration in benzene. The results obtained reveal that the large, positive amplitude of the field-induced dielectric increment (Δε≈10^{-3}) and its frequency dependence observed in the nonlinear dielectric effect spectra, even far from the possible isotropic-smectic A type phase transition, are due to short range fluctuations of the electric moment. The nature of molecular formations as a result of the strong intermolecular orientational correlations is discussed.

6

Magnetic Stripes on Hexagonal Lattice with Competing Exchange and Dipole-Dipole Interactions

80%

Joknys A., Tornau E.

Acta Physica Polonica A

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2008

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vol. 113

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issue 3

951-954

EN

We obtained the phase diagram for the Ising model with competing exchange and dipolar interactions on 2D hexagonal lattice. By using histogram method we determined the order of the phase transition from isotropic stripe phase to low-temperature anisotropic stripe phases AFh of different stripe widths h. The first order phase transition was found to AF1 and AF2 phases and the second order - to AF3 and AF4 phases. We have also found that in AF1 phase stripe domain grows with time as t^{0.5}. In phases AF3 and AF4 stripe domain growth is proportional to log t.

7

Review of Surface Relaxation and Reconstruction Phenomena

80%

Zieliński P.

Acta Physica Polonica A

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1996

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vol. 89

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issue 2

251-263

EN

The basic definitions concerning structure of surface are given. The principal experimental methods of the observation of surfaces are reviewed. A possibly heuristic explanation is given of principal theoretical concepts underlying the present understanding of the surface phenomena. The best known and/or understood examples of the surface relaxation, surface reconstruction and roughening are reviewed.

8

High Temperature Magnetic and Thermal Properties of (Pb_ySn_{1-y})_2P_2S_6 Chalcogenides

80%

Il'kovič S., Reiffers M., Šebeň V., Šterbáková K., Burger V., Parma L., Čobal' O., Rizak I., Rizak V.

Acta Physica Polonica A

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2012

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vol. 122

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issue 1

12-14

EN

The results of study of Pb influence on high temperature magnetic and thermal properties of the chalcogenides (Pb_ySn_{1-y})_2P_2S_6 are presented. The increasing Pb content shifts phase transition to the ferroelectric state at about 337 K towards lower temperatures while magnetic field till 3 T has no influence on this transition. The measured susceptibility and magnetisation data are discussed.

9

Growth Analysis and Numerical Simulation of Cu_3BiS_3 Absorbing Layer Solar Cell through the wxAMPS and Finite Element Method

80%

Mesa F., Ballesteros V., Dussan A.

Acta Physica Polonica A

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2014

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vol. 125

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issue 2

385-387

EN

The properties and the efficiency of a semiconductor thin film depend on the state of stress and defects in the film structure. When the film is growing layer by layer, the elastic energy due to deformation stress between the substrate and the film is released partly due to the formation of dislocations in the critical thickness deformation. In this paper, we present a finite element analysis of the stress state in a thin film of Cu_3BiS_3 as a function of thickness and elastic energy release by nucleation of dislocations. Initially, we analyze the stress contours associated with the epitaxial growth and dislocation nucleation and then combine these two in order to study the effective potential energy state of the system. Finally, the tool wxAMPS is today an important application for simulation of solar cells with high reliability and an improved design over its analysis of microelectronic and photonic structures predecessor, incorporating physical principles concerning photovoltaic phenomena and uses a new method for solving algorithms, combining Newton and Gummel approaches, which provides greater stability and speed of computation.

10

The Phase Diagrams of Spin-1/2 Ising Model on a Two-Layer Bethe Lattice with AFM/AFM Interactions

80%

Albayrak E., Yigit A.

Acta Physica Polonica A

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2009

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vol. 116

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issue 2

127-134

EN

The phase diagrams of spin-1/2 Ising model on a two-layer Bethe lattice with antiferromagnetic interactions for each layer and either antiferromagnetic or ferromagnetic interaction between the layers are investigated by using the pairwise approach for given values of coordination number q. The exact expressions of the order-parameters, response functions and free energy are obtained in terms of the recursion relations. The ground-state phase diagrams are calculated for given system parameters of the model. In the guidance of the ground-state phase diagrams, the temperature dependent phase diagrams of the model are also studied in detail for given coordination numbers q = 3, 4 and 6. It was found that the system presents only second-order phase transitions with different thermal behaviors for all values of q. In addition, two Néel temperatures, T_{N}, are found for q = 6 only.

11

Surface Investigations of Selected Materials by Low-Energy Ion Scattering Technique

80%

Goc-Jagło D., Sitko D., Jagło G., Kim-Ngan N., Soszka W.

Acta Physica Polonica A

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2007

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vol. 111

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issue 5

763-771

EN

Surfaces of three selected materials were investigated by means of low-energy ion-scattering technique: (1) the magnetite (Fe_3O_4) exhibiting the so-called Verwey transition (T_V(bulk)=125 K) accompanied by a small cubic-monoclinic crystal distortion, (2) the intermetallic compound NdMn_2 undergoing an antiferromagnetic-paramagnetic phase transition (T_N=104 K) accompanied by a large crystal distortion with a volume change of 1%, and (3) the typical insulator BaTiO_3 with two structural transitions below 300 K. The primary energy of the (Ne^+, Ar^+) ion beam was in the range of 4-8 keV, and the low-energy ion-scattering spectra were collected in the temperature range of 85-300 K. A large influence from the Verwey transition on the neutralization and re-ionization of scattered ions from magnetite surface was observed, while no visible change at the magnetic phase transition in NdMn_2 was revealed in the low-energy ion-scattering spectra. A strong dependence of the characteristics of the low-energy ion-scattering spectra on the irradiated time was observed for BaTiO_3 indicating that this surface was heavily charged by ion bombardments.

12

Photo-Induced Structural Changes at a Surface οf Organic Single Crystals Observed by Vibrational Sum Frequency Generation Spectroscopy

80%

Fukumoto K., Fukazawa N., Ishikawa T., Koshihara S., Yamamoto H., Kato R., Onda K.

Acta Physica Polonica A

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2012

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vol. 121

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issue 2

313-315

EN

Phase transitions from insulator to metal induced by thermal excitation and by photo-irradiation at the surface of β'-(BEDT-TTF)(TCNQ) are investigated using vibrational sum frequency generation spectroscopy. The results are compared with linear reflectivity measurements which detect the information mainly from bulk. IR absorption spectra of a_{g} vibrational modes of TCNQ induced by the dimerization are observed using vibrational sum frequency generation spectroscopy, and its intensity is found to become smaller by thermal excitation indicating the transition to the metal phase. Time-dependent degree of dimerization is also observed by pump-probe experiments with almost the same statistics as the static measurements. On the other hand, in the reflectivity experiments, the reduction of dimerization is also observed by elevating the temperature, however, the spectral shapes are deformed for the time-resolved measurements. These results imply that the different dynamics occur at the surface and in the bulk.

13

Nonlinear Dielectric Relaxation in Solutions of the Polar Mesogenic Molecules in the Isotropic Phase

80%

Kędziora P.

Acta Physica Polonica A

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2003

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vol. 104

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issue 1

45-53

EN

The nonlinear spectra of 4,4'-n-hexylcyanobiphenyl (C_6H_{13}-Ph-Ph-CN) in benzene solutions were recorded in the frequency range of 300~kHz-100~MHz in the presence of the strong static electric field E_0=1.1×10^7 V/m, at 25˚C. The dynamic pretransitional phenomena revealed for polar C_6H_{13}-Ph-Ph-CN were interpreted in the frame of the Landau-de Gennes theory. The identical concentration-dependent behavior of nonlinear relaxation time in the vicinity of the transition from the isotropic to the nematic phase for polar and nonpolar compounds was discussed.

14

On the Temperature-Dependent Surface Structure of Metals

80%

Bonzel H., Breuer U.

Acta Physica Polonica A

|

1992

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vol. 81

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issue 2

265-272

EN

Recent experimental results based on X-ray photoelectron diffraction from a Pb(110) crystal are discussed in terms of surface roughening and surface melting. In comparison to other reports on Pb(110) surface roughening it is recognized that the correct determination of the roughening transition on (110) surfaces of fcc metals may be intrinsically difficult because of anisotropy. A novel technique for investigating the temperature-dependent surface free energy is described. The method involves the quasi-steady-state shape of periodic surface profiles on Au(111) and Au(100) single crystals. First results are reported for two crystallographic zones (111)⟨112⟩ and (100)⟨110⟩ of Au. These results illustrate the strong anisotropy of Δγ/γ of ~23% and ~ 4% at T = 0 K for the (111)⟨112⟩ and (100)⟨110⟩ zones, respectively. The data suggest that the low-index surfaces of Au(111) and (100) are not likely to roughen at T ≤ T_{M}.

15

Size Effects in Radiospectroscopy Spectra of Ferroelectric Nanopowders

80%

Glinchuk M., Kondakova I., Laguta V., Slipenyuk A., Bykov I., Ragulya A., Klimenko V.

Acta Physica Polonica A

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2005

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vol. 108

|

issue 1

47-60

EN

The theoretical and experimental investigation of ferroelectric nanopowders is performed. The manifestation in radiospectroscopy spectra of size driven ferroelectric-paraelectric phase transition at some critical particle average size R = R_c was the main goal of the consideration. In theoretical part the size effect for the materials with ferroelectric tetragonal phase at room temperature and cubic paraelectric phase was considered allowing for the spontaneous polarization inhomogeneity inside a particle and distribution of particle sizes. In ESR the transformation of the spectra from tetragonal symmetry to cubic symmetry lines with decrease in nanoparticle sizes was calculated. The method of R_c value extraction from the ratio of the different symmetry lines intensities in the absorption spectra was proposed. Measurements of Fe^{3+} ESR spectra in nanopowder of BaTiO_3 were carried out at room temperature. The samples were prepared by rate-controlled method with different particle sizes, which depend on annealing temperature. The decrease in intensity of tetragonal symmetry ESR lines of Fe^{3+} and appearance of cubic symmetry line with asymmetry of the shoulders was observed with the average sizes decrease with complete disappearance of tetragonal spectrum at R ≤ 40 nm. The comparison of the theory with experiment was carried out. The theory fits experimental data pretty good. The value of critical size R_c ≈ 40 nm was extracted from ESR data. The asymmetry and broadening of right hand side shoulder of ESR cubic symmetry line was shown to be related to contribution of paramagnetic centers in the vicinity of the particles surface with lower than cubic symmetry. The deconvolution of the cubic line allowed to show that this region size is about 3 nm.

16

Anomalous Dielectric Relaxation in Binary Mixtures of Mesogenic Solvent/Non-Mesogenic Solute

70%

Jadżyn J., Bauman D., Déjardin J., Ginovska M., Czechowski G.

Acta Physica Polonica A

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2005

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vol. 108

|

issue 3

479-489

EN

Dielectric relaxation studies for mixtures of strongly polar and mesogenic n-heptylcyanobiphenyl with non-polar and non-mesogenic carbon tetrachloride (CCl_4) were performed. The absorption band broadening due to fractional diffusion was observed. A correlation between the non-mesogenic admixture concentration and the anomalous diffusion exponent was found.

17

Molecular Dynamics of Tert-butyl Chloride Confined to CPG (7.4, 15.6 nm)

70%

Szutkowska L., Peplińska B., Jurga S.

Acta Physica Polonica A

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2005

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vol. 108

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issue 2

357-370

EN

The paper complements our earlier NMR investigation of molecular dynamics of tert-butyl chloride restricted by geometries of the type MCM-41 and CPG by the new sizes of CPG and by differential scanning calorimetry method. We report proton and deuteron NMR lineshapes and the spin-lattice relaxation results of tert-butyl chloride in CPG of the 15.6 nm and 7.4 nm pore diameter in the temperature range 70 K≤ T≤ 292 K. The bulk-like component of the confined tert-butyl chloride, in temperatures corresponding to phase III, is interpreted as a composition of two dynamically different subphases. The parameters of motions of both subphases are derived. The tert-butyl group motion in both subphases is more restricted than in the bulk tert-butyl chloride, although the activation energies are lower. Differential scanning calorimetry was used to determine temperatures of the phase transitions (140 K≤T≤292 K). The results show that the depression of the phase transition temperature is pore size dependent and that the confinement has less influence on transition to the plastic phase than on the freezing and on the solid II - solid III transition.

18

Phase transitions in the adsorbed molecular chains

61%

Lykah V., Syrkin E.

Open Physics

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2005

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vol. 3

|

issue 1

61-68

EN

Rotational excitations of molecular adsorbed layers are studied theoretically. Nonlinear dynamical equations are obtained with accounting of quadrupolar interactions between molecules and freezing of translational degrees of freedom. The equilibrium positions of the molecules are found to be experimentally observed structures with alternating rotational ordering of planar rotors along the direction to the nearest neighbor (for linear or square structures) under low temperature. Dynamical analysis gives an integral of motion (energy) of the chain that in the long-wave limit leads consequently to the existence of four phases. The first one corresponds to oscillations near equilibrium ordered states. The second phase corresponds to low-energy rotational excitations along ‘valleys’ (easy directions in the effective potential) that do not destroy strong correlations between molecules while structural data can show rotational disorder (melting). The third phase corresponds to an energy that is enough to travel between ‘valleys’; only some ‘islands’ in the angle space are forbidden. Complete destruction of correlation when the energy is over the peaks of the effective potential corresponds to the fourth phase. Therefore rotational melting is a complex phenomenon that has several stages.

Refine search results

The Spin-1/2 Ising Model on the Bow-Tie Lattice as an Exactly Soluble Free-Fermion Model

Reentrant Transitions of Ising-Heisenberg Ferromagnet on a Triangular Lattice with Diamond-Like Decorations

Composition and Order-Disorder Transition in the Cu_3Au (001) Surface Layer Investigated with the Use of DAES and DEPES

Directional Auger Electron Spectroscopy - Possibilities, Limitations and Proposal of Improvements

Short-Range Order Fluctuation in the Isotropic Phase of Solutions of 4-trans-4'-n-dodecylcyanobiphenyl in Benzene Studied by Nonlinear Dielectric Spectroscopy

Magnetic Stripes on Hexagonal Lattice with Competing Exchange and Dipole-Dipole Interactions

Review of Surface Relaxation and Reconstruction Phenomena

High Temperature Magnetic and Thermal Properties of (Pb_ySn_{1-y})_2P_2S_6 Chalcogenides

Growth Analysis and Numerical Simulation of Cu_3BiS_3 Absorbing Layer Solar Cell through the wxAMPS and Finite Element Method

The Phase Diagrams of Spin-1/2 Ising Model on a Two-Layer Bethe Lattice with AFM/AFM Interactions

Surface Investigations of Selected Materials by Low-Energy Ion Scattering Technique

Photo-Induced Structural Changes at a Surface οf Organic Single Crystals Observed by Vibrational Sum Frequency Generation Spectroscopy

Nonlinear Dielectric Relaxation in Solutions of the Polar Mesogenic Molecules in the Isotropic Phase

On the Temperature-Dependent Surface Structure of Metals

Size Effects in Radiospectroscopy Spectra of Ferroelectric Nanopowders

Anomalous Dielectric Relaxation in Binary Mixtures of Mesogenic Solvent/Non-Mesogenic Solute

Molecular Dynamics of Tert-butyl Chloride Confined to CPG (7.4, 15.6 nm)

Phase transitions in the adsorbed molecular chains