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1.
The magnetic properties of a ferromagnetic thin film of face centered cubic (FCC) lattice with Heisenberg spin-S are examined using the high-temperature series expansions technique extrapolated with Padé approximations method. The critical reduced temperature of the system τc is studied as function of thickness of the film and the exchange interactions in the bulk, and within the surfaces Jb, Js and J⊥ respectively. A critical value of surface exchange interaction above which surface magnetism appears is obtained. The dependence of the reduced critical temperature on the film thickness L has been investigated. 相似文献
2.
The phase transition properties of ferroelectric supperlattice with finite alternating layers have been investigated by using the transverse Ising model within the mean field approximation. The effects of surface modification are introduced on the assumption that the exchange interaction and transverse field parameters on the top surface are different from those in other layers of the superlattice. The phase diagrams are described in two different ways. The results indicate that the features of the phase diagrams can be greatly modified by changing the transverse Ising model parameters. 相似文献
3.
The phase diagrams of ferroelectric thin films with two surface layers described by the transverse Ising model have been studied under the mean-field approximation. We discuss the effects of the exchange interaction and transverse field parameters on the phase diagrams. The results indicate that the phase transition properties of the phase diagrams can be greatly modified by changing the transverse Ising model parameters. In addition, the crossover features of the parameters from the ferroelectric dominant phase diagram to the paraelectric dominant phase diagram are determined for ferroelectric thin films with two surface layers. 相似文献
4.
The stability of a spin-glass (SG) phase is analyzed in detail for a fermionic Ising SG (FISG) model in the presence of a magnetic transverse field Γ. The fermionic path integral formalism, replica method and static approach have been used to obtain the thermodynamic potential within one step replica symmetry breaking ansatz. The replica symmetry (RS) results show that the SG phase is always unstable against the replicon. Moreover, the two other eigenvalues λ± of the Hessian matrix (related to the diagonal elements of the replica matrix) can indicate an additional instability to the SG phase, which enhances when Γ is increased. Therefore, this result suggests that the study of the replicon cannot be enough to guarantee the RS stability in the present quantum FISG model, especially near the quantum critical point. In particular, the FISG model allows changing the occupation number of sites, so one can get a first order transition when the chemical potential exceeds a certain value. In this region, the replicon and the λ± indicate instability problems for the SG solution close to all ranges of a first order boundary. 相似文献
5.
Monte Carlo simulations of a sheared Ising model are used to study nonequilibrium fluctuations of mechanical work. The validity of the transient (starting from equilibrium) and the steady state fluctuation relations is verified. A fluctuation relation has been also shown to hold for the mechanical work done on the system, during the transition between two nonequilibrium steady states corresponding to different drivings. 相似文献
6.
Mixed spin transverse Ising model with longitudinal random crystal field interactions 总被引:1,自引:0,他引:1
N. Benayad R. Zerhouni A. Klümper 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):687-695
The effect of a longitudinal random crystal field interaction on the phase diagrams of the mixed spin transverse Ising model
consisting of spin-1/2 and spin-1 is investigated within the finite cluster approximation based on a single-site cluster theory.
In order to expand a cluster identity of spin-1, we transform the spin-1 to spin-1/2 representation containing Pauli operators.
We derive the state equations applicable to structures with arbitrary coordination number N. The phase diagrams obtained in the case of a honeycomb lattice (N=3) and a simple-cubic lattice (N=6), are qualitatively different and examined in detail. We find that both systems exhibit a variety of interesting features
resulting from the fluctuation of the crystal field interactions.
Received: 13 February 1998 / Accepted: 17 March 1998 相似文献
7.
We consider a flower-like Ising model, in which there are some additional bonds (in the “flower-core”) compared to a pure
Ising chain. To understand the behaviour of this system and particularly the competition between ferromagnetic (usual) bonds
along the chain and antiferromagnetic (additional) bonds across the chain, we study analytically and iteratively the main
thermodynamic quantities. Very interesting is, in the zero-field and zero-temperature limit, the behaviour of the magnetization
and the susceptibility, closely related to the ground state configurations and their degeneracies. This degeneracy explains
the existence of non-zero entropy at zero temperature, in our results. Also, this model could be useful for the experimental
investigations in studying the saturation curves for the enzyme kinetics or the melting curves for DNA-denaturation in some
flower-like configurations. 相似文献
8.
The features of order in narrow systems are studied for isotropic square lattice Ising models with general parabolic boundaries. Using Monte Carlo methods, magnetization profiles are calculated which agree very well with the conformal results and scale properly with the geometrical length parameter. The variation of the tip magnetization with temperature is obtained and the predicted stretched exponential form in the critical region is confirmed. 相似文献
9.
The critical temperature of layered Ising models on triangular and honeycomb lattices are calculated in simple, explicit form
for arbitrary distribution of the couplings. 相似文献
10.
In the vicinity of boundaries the bulk universality class of critical phenomena splits into several boundary universality classes, depending upon whether the tendency to order in the boundary is smaller or larger than in the bulk. For Ising universality class there are five different boundary universality classes: periodic, antiperiodic, free, fixed and mixed (mixture of the last two). In this paper we present the new set of the universal amplitude ratios for the mixed boundary universality class. The results are in perfect agreement with a perturbated conformal field theory scenario proposed by Cardy [J. Cardy, Nucl. Phys. B 270 (1986) 186]. 相似文献
11.
The magnetic properties of a mixed Ising ferrimagnetic system, in which the two interacting sublattices have spins σ, (±1/2) and spins S, (±1,0) in the presence of a random crystal field, have been studied with the mean field approach. The obtained results show the existence of some interesting phenomena, such as the appearance of a new ferrimagnetic phase, namely, partly ferrimagnetic phase and consequently the existence of four topologically different types of phase diagrams. Furthermore, compensation behaviour and re-entrant phenomenon are found for appropriate ranges of crystal field. Thermal magnetization behaviour and phase diagrams have been discussed in detail. 相似文献
12.
An Ising model with ferromagnetic nearest-neighbor interactions J1 (J1>0) and random next-nearest-neighbor interactions [+J2 with probability p and −J2 with probability (1−p); J2>0] is studied within the framework of an effective-field theory based on the differential-operator technique. The order parameters are calculated, considering finite clusters with n=1,2, and 4 spins, using the standard approximation of neglecting correlations. A phase diagram is obtained in the plane temperature versus p, for the particular case J1=J2, showing both superantiferromagnetic (low p) and ferromagnetic (higher values of p) orderings at low temperatures. 相似文献
13.
Jun Wang 《Physica A》2009,388(5):565-573
We investigate the correlation inequalities and the decay of correlations of stochastic Ising model in a rectangle with side length 2L×K(LlnL)1/2, where K is some positive constant. With different boundary conditions, at inverse temperature β>βc or β<βc and zero external field, we show some estimates of the correlation functions for the two-dimensional Ising model. 相似文献
14.
Pb0.97La0.02(Zr0.85Sn0.13Ti0.02)O3 (PLZST 2/85/13/2) antiferroelectric thin films were deposited on Pt(111)/Ti/SiO2/Si and LaNiO3(LNO)/SiO2/Si substrates through a modified sol-gel process. The phase structure and microstructure of PLZST 2/85/13/2 antiferroelectric thin films were analysed by x-ray diffraction (XRD), scanning electron microcopy (SEM) and field-emission SEM (FE-SEM). The antiferroelectric nature of the PLZST 2/85/13/2 thin films on two electrodes was demonstrated by the C-V (capacitance-voltage) and P-E (polarization-electric field) measurement. The maximum polarizations for PLZST 2/85/13/2 films on Pt and LNO electrodes were 42 and 18 μC/cm2, respectively. The temperature dependence of the dielectric property of the PLZST 2/85/13/2 films was measured under different dc electric fields. Also, the phase transformation of the PLZST 2/85/13/2 films was studied in detail as a function of temperature and dc electric field. 相似文献
15.
A. Saber G. Mattei X. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):393-399
Within the framework of the effective field theory with a probability distribution technique that accounts for the single-site
spin correlations, we examine the critical behavior of the transverse ferromagnetic spin-1 Ising model of an alternating magnetic
superlattice. The critical temperature of the alternating magnetic superlattice has been studied as a function of the interlayer
and intralayer exchange interactions and the strength of the transverse field and the thickness of the finite superlattice.
Received 12 January 2000 and Received in final form 14 September 2000 相似文献
16.
Ferroelectric Properties of Polycrystalline Ceramics with Dipolar Defect Simulated from the Potts--Ising Model 下载免费PDF全文
Physical properties of polycrystailine ferroelectrics including the contributions of the fixed dipolar defects and the average grain size in the Potts-Ising model are simulated by using the Monte Carlo method. Domain pattern, hysteresis loop and switching current of the polarization reversal process are obtained. Two processes are considered in our simulation. In the first one, the grain texture of ferroelectric ceramics are produced from the Ports model, and then the Ising model is implemented in the obtained polycrystailine texture to produce the domain pattern, hysteresis loop and switching current. It is concluded that the defect has the ability to decrease the remnant polarization P~ as well as the coercive field E~. The back switching is obviously observed after the electric field is off, and it shows some variation after introducing the fixed dipolar defect. Meanwhile, the spike of the switching current is found to lower with the increasing defect concentration and the decreasing average grain size. 相似文献
17.
S. G. Magalhães F. M. Zimmer C. J. Kipper E. J. Calegari 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):209-218
The competition among spin glass (SG), antiferromagnetism (AF)
and local pairing superconductivity (PAIR) is studied in a two-sublattice fermionic Ising spin glass model with a local BCS
pairing interaction in the presence of an applied magnetic transverse field Γ. In the present approach, spins in different
sublattices interact with a Gaussian random coupling with an antiferromagnetic mean J0 and standard deviation J.
The problem is formulated in the path integral formalism in which spin operators are represented by
bilinear combinations of Grassmann variables. The saddle-point Grand Canonical potential
is obtained within the static approximation and the replica symmetric ansatz. The results are analysed in phase diagrams in
which the AF and the SG phases can occur for small g (g is the strength of the local superconductor coupling written in units
of J), while the PAIR phase appears as unique solution for large g. However, there is a complex line transition separating
the PAIR phase from the others. It is second order at high temperature that ends in a tricritical point. The quantum fluctuations
affect deeply the transition lines and the tricritical point due to the presence of Γ. 相似文献
18.
Indrani Coondoo 《Solid State Communications》2007,142(10):561-565
Europium substituted samples of the compositions Sr1−xEuxBi2Ta2O9 (x=0.0,0.025,0.050,0.10 and 0.20) were synthesized by solid state reaction method and studied for their structural, dielectric and ferroelectric properties. The X-ray diffractograms confirmed the formation of single phase layered perovskite structure in all the samples. The temperature variation of dielectric constant shows that the Curie temperature (Tc) decreases on increasing concentration of europium. The dielectric loss reduces significantly with europium addition. The P-E studies of the Eu-substituted SBT ceramics show that the remanent polarization increases with increasing concentration of europium. 相似文献
19.
EPR study of the low temperature ferroelectric phase transition in Cu doped Rb2ZnCl4 single crystals
Mariana Stefan Sergiu V. Nistor Dirk SchoemakerIoan Ursu 《Solid State Communications》2003,127(11):695-698
Temperature dependent EPR measurements on copper doped Rb2ZnCl4 single crystals allowed us to evidence and study the P21cn↔C1c1 structural phase transition that takes place in this compound at 74.6 K. From the two types of Cu2+ centers localized at different anionic sites, called Cu2+(I) and Cu2+(II), which are formed in this compound, only the Cu2+(II) centers exhibit observable changes in their EPR spectra, attributable to the symmetry lowering. The observed changes have been related to the soft-mode responsible for the structural phase transition. 相似文献
20.
The single-cluster Monte Carlo algorithm and the reweighting technique are used to simulate the 3D ferromagnetic Ising model on 3D Voronoi-Delauney lattices. It is assumed that the coupling factor J varies with the distance r between the first neighbors as J(r)∝e−ar, with a≥0. The critical exponents γ/ν, β/ν, and ν are calculated, and according to the present estimates for the critical exponents, we argue that this random system belongs to the same universality class of the pure 3D ferromagnetic Ising model. 相似文献