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1.
An improved transverse Ising model is proposed by taking the
depolarization field effect into account. Within the framework of
mean-field theory we investigate the behavior of the ferroelectric thin
film. Our results show that the influence of the depolarization field
is to flatten the spontaneous polarization profile and make the films
more homogeneous, which is consistent with Ginzburg-Landau theory.
This fact shows that this model can be taken as an effective model to
deal with the ferroelectric film and can be further extended to refer
to quantum effect. The competition between quantum effect and
depolarization field induces some interesting phenomena on ferroelectric thin films. 相似文献
2.
A transverse Ising spin system, in the presence of time-dependentlongitudinal field, is studied by the effective-field theory (EFT). Theeffective-field equations of motion of the average magnetization are givenfor the simple cubic lattice (Z = 6) and the honeycomb lattice (Z = 3).The Liapunov exponent λ is calculated for discussing the stability of the magnetization and it is used to determine the phase boundary. Thedynamic phase transition diagrams in h0/ ZJ -Γ/ZJ plane and in h0/ZJ-T/ZJ plane have been drawn, and there is no dynamical tricritical point on the dynamic phase transition boundary. The effect of the thermal fluctuations upon the dynamic phase boundary has been discussed. 相似文献
3.
The crystal-field effect of spin-3/2 transverse Ising model is studied with the scheme of mean-field approximation. The influences of the crystal field and the transverse field on the phase diagram of the system are discussed. 相似文献
4.
We study critical behaviors of the reduced fidelity susceptibility for two neighboring sites in the onedimensional transverse field Ising model. It is found that the divergent behaviors of the susceptibility take the form of square of logarithm, in contrast with the global ground-state fidelity susceptibility which is power divergence. In order to perform a scaling analysis, we take the square root of the susceptibility and determine the scaling exponent analytically and the result is further confirmed by numerical calculations. 相似文献
5.
The phase diagrams of a spin-2 transverse Ising model with a random field on honeycomb, square, and simple-cubic lattices, respectively, are investigated within the framework of an effective-field theory with correlations.We find the behavior of the tricritical point and the reentrant phenomenon for the system with any coordination number z, when the applied random field is bimodal. The behavior of the tricritical point is also examined as a function of applied transverse field. The reentrant phenomenon comes from the competition between the transverse field and the random field. 相似文献
6.
Influence of lateral size on dielectric properties of ferroelectric thin films with structure transition zones 下载免费PDF全文
By taking into account structural transition zones near the lateral
and thickness direction edges, this paper uses a modified transverse
Ising model to study dielectric properties of a finite size
ferroelectric thin film in the framework of the mean-field
approximation. The results indicate that the influence of the
lateral size on the dielectric susceptibility cannot be neglected
and lateral structural transition zones could be a crucial factor
that improves the mean susceptibility of the fixed size film. 相似文献
7.
By using the simple decoupling approximation to Fermi-type Green's functionfor the transverse Ising model under pseudospin theory, we systemicallystudy the influence of different exchange interactions (transverse fields)of the two distinct materials on the polarization and Curie temperature offinite alternating superlattice. Meanwhile, we analyze the effect of thewhole parameters of the top surface, present their influence on thepolarization of each layer (including the mean polarization of the wholeferroelectric superlattice) and on the Curie temperature. The results showthe ratio of the exchange interactions (the transverse fields), which are ofthe two alternating materials have deeply impact on the polarization andCurie temperature of the supperlattice. Moreover, the top surface also hasgreat influence on the whole ferroelectric superlattice. 相似文献
8.
9.
The transverse spin-2 Ising ferromagnetic model with a longitudinal crystal field is studied within the mean-field theory. The phase diagrams and magnetization curves are obtained by diagonalizing the Hamiltonian Hi of the Ising system numerically, and the first order-order phase transitions, the first order-disorder phase transitions, and the second-order phase transitions are discussed in details. Reentrant phenomena occur when the value of the transverse field is not zero and the reentrant diagram is given. 相似文献
10.
The transverse spin-2 Ising ferromagnetic model with a longitudinal crystal field is studied within the mean-field theory. The phase diagrams and magnetization curves are obtained by diagonalizing the Hamiltonian Hi of the Ising system numerically, and the first order-order phase transitions, the first order-disorder phase transitions, and the second-order phase transitions are discussed in details. Reentrant phenomenaoccur when the value of the transverse field is not zero and the reentrantdiagram is given. 相似文献
11.
In this paper we show how an infinite system of coupled Toda-type nonlinear differential equations derived by one of us can
be used efficiently to calculate the time-dependent pair-correlations in the Ising chain in a transverse field. The results
are seen to match extremely well long large-time asymptotic expansions newly derived here. For our initial conditions we use
new long asymptotic expansions for the equal-time pair correlation functions of the transverse Ising chain, extending an old
result of T.T. Wu for the 2d Ising model. Using this one can also study the equal-time wavevector-dependent correlation function
of the quantum chain, a.k.a. the q-dependent diagonal susceptibility in the 2d Ising model, in great detail with very little computational effort.
Supported in part by the National Science Foundation under grant PHY 07-58139 and by the Australian Research Council under
Project ID: LX0989627. 相似文献
12.
13.
Ground-State Phase Diagram of Transverse Spin-2 Ising Model with Longitudinal Crystal-Field 总被引:2,自引:0,他引:2
The transverse spin-2 Ising ferromagnetic model with a longitudinal crystal-field is studied within the mean-field theory based on Bogoliubov inequality for the Gibbs free energy. The ground-state phase diagram and the tricritical point are obtained in the transverse field Ω/z J-longitudinal crystal D/zJ field plane. We find that there are the first order-order phase transitions in a very smallrange of D/zJ besides the usual first order-disorder phase transitions and the second order-disorder phase transitions. 相似文献
14.
The magnetocaloric response of the mixed spin-1/2 and spin-S () Ising model on a decorated square lattice is thoroughly examined in presence of the transverse magnetic field within the generalized decoration-iteration transformation, which provides an exact mapping relation with an effective spin-1/2 Ising model on a square lattice in a zero magnetic field. Temperature dependencies of the entropy and isothermal entropy change exhibit an outstanding singular behavior in a close neighborhood of temperature-driven continuous phase transitions, which can be additionally tuned by the applied transverse magnetic field. While temperature variations of the entropy display in proximity of the critical temperature a striking energy-type singularity , two analogous weak singularities can be encountered in the temperature dependence of the isothermal entropy change. The basic magnetocaloric measurement of the isothermal entropy change may accordingly afford the smoking gun evidence of continuous phase transitions. It is shown that the investigated model predominantly displays the conventional magnetocaloric effect with exception of a small range of moderate temperatures, which contrarily promotes the inverse magnetocaloric effect. It turns out that the temperature range inherent to the inverse magnetocaloric effect is gradually suppressed upon increasing of the spin magnitude S. 相似文献
15.
Lu Zhao-Xin 《Phase Transitions》2016,89(3):273-282
The magnetic properties of a hexagonal transverse Ising nanoisland have been calculated by the effective-field theory with correlations. The effects of surface coupling, interlayer coupling, and the competition between transverse fields at the surface shell and in the inner core on phase diagrams and magnetizations are examined. Meanwhile, the results are also compared with two different nanoislands which consist of two layers with nine atoms or five atoms in each of the layers. 相似文献
16.
T. Kaneyoshi 《Phase Transitions》2015,88(2):121-136
The phase diagrams and temperature dependences of magnetizations in ultra-thin transverse Ising thin films are studied by the use of both the effective-field theory with correlations (EFT) and the mean-field theory (MFA). Novel features, such as the possibility of re-entrant phenomena, are obtained for the magnetic properties in such systems with a zero transverse field at the surfaces, when the EFT is applied to them, although such features could not be found from the use of the MFA. When the transverse field at the surfaces takes a finite value, however, the re-entrant phenomena could not be found from the both formulations of the EFT and the MFA. Similar phenomena are then obtained in the phase diagrams by using the MFA and the EFT. 相似文献
17.
T. Kaneyoshi 《Phase Transitions》2013,86(6):603-612
The phase diagram and magnetizations in a transverse Ising nanoisland are examined by using the effective field theory with correlations. The nanoisland is constructed from two layers with nine atoms in each which are coupled by the interlayer coupling. We present some characteristic phenomena in them which come from the frustration induced by an interlayer coupling and two transverse fields. 相似文献
18.
An elastic Ising model for a one-dimensional diatomic spin chain is proposed to explain the ferroelectricity induced by the collinear magnetic order with a low-excited energy state. A statistical theory based on this model is developed to calculate the electrical and magnetic properties of Ca3CoMnO6, a typical quasi-one-dimensional diatomic spin chain system. The calculated ferroelectric polarization and dielectric susceptibility show a good agreement with recently reported data on Ca3Co2-xMnxO6 (x ≈0.96) (Phys. Rev. Lett. 100 047601 (2008)), although the predicted magnetic susceptibility does not coincide well with experiment. We also address the rationality and deficiency of this model by including a first-order correction which improves the consistency between the model and experiment. 相似文献
19.
The magnetic properties of the bond-diluted spin-3/2 transverse Ising model with the presence of a crystalfield on the honeycomb lattice are studied within the framework of the effective field theory with correlations. Theinteractions Jij are assumed to be independent random variables with distribution P(Jij) = pδ(Jij - J) + (1 - P)δ(Jij). 相似文献
20.
T. Kaneyoshi 《Phase Transitions》2013,86(11):995-1008
The phase diagram and magnetizations of a cylindrical nanotube described by the transverse Ising model are investigated by the use of the effective field theory with correlations. Some comparisons between the nanotube and the nanowire have been given for the phase diagrams. In particular, the temperature dependences of longitudinal magnetization in the system with a negative shell–core interaction are investigated. Some characteristic phenomena (new types in ferrimagnetism) which have not been observed in the nanowire as well as similar phenomena are found in the thermal variations, depending on the ratio of the physical parameters in the surface shell and the core. The possibilities of two compensation points and a field induced compensation point in the nanotube are also discussed. 相似文献