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71.
By using the Quantum Monte Carlo simulation; the electric properties of a nanowire, consisting of a ferroelectric core of spin-1/2 surrounded by a ferroelectric shell of spin-1/2 with ferro- or anti-ferroelectric interfacial coupling have been studied within the framework of the Transverse Ising Model (TIM). We have examined the effects of the shell coupling Js, the interfacial coupling JInt, the transverse field Ω, and the temperature T on the hysteresis behavior and on the electric properties of the system. The remanent polarization and the coercive field as a function of the transverse field and the temperature are examined. A number of characteristic behavior have been found such as the appearance of triple hysteresis loops for appropriate values of the system parameters. 相似文献
72.
73.
Ya-Qiu Liang Guo-Zhu Wei Xiao-Juan Xu 《Journal of magnetism and magnetic materials》2010,322(15):2219-2222
A two-sublattice Ising metamagnet in both uniform and random fields is studied within the mean-field approach based on Bogoliubov’s inequality for the Gibbs free energy. We show that the qualitative features of the phase diagrams are dependent on the parameters of the model and the uniform field values. The tricritical point and reentrant phenomenon can be observed on the phase diagram. The reentrance is due to the competition between uniform and random interactions. 相似文献
74.
W. P. Orrick B. Nickel A. J. Guttmann J. H. H. Perk 《Journal of statistical physics》2001,102(3-4):795-841
We have made substantial advances in elucidating the properties of the susceptibility of the square lattice Ising model. We discuss its analyticity properties, certain closed form expressions for subsets of the coefficients, and give an algorithm of complexity O(N6) to determine its first N coefficients. As a result, we have generated and analyzed series with more than 300 terms in both the high- and low-temperature regime. We quantify the effect of irrelevant variables to the scaling-amplitude functions. In particular, we find and quantify the breakdown of simple scaling, in the absence of irrelevant scaling fields, arising first at order |T–Tc|9/4, though high-low temperature symmetry is still preserved. At terms of order |T–Tc|17/4 and beyond, this symmetry is no longer present. The short-distance terms are shown to have the form (T–Tc)p (log |T–Tc|)q with pq2. Conjectured exact expressions for some correlation functions and series coefficients in terms of elliptic theta functions also foreshadow future developments. 相似文献
75.
G. Schröder T. Knetter M.J. Alava H. Rieger 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(1):101-105
Random walk arguments and exact numerical computations are used to study one-dimensional random field chains. The ground state
structure is described with absorbing and non-absorbing random walk excursions. At low temperatures, the local magnetization
follows the ground state except at regions where a local random field fluctuation makes thermal excitations easier. This is
explained by the random walk picture, implying that the magnetization lengthscale is a product of the domain size and the
thermal excitation scale.
Received 16 October 2000 and Received in final form 7 June 2001 相似文献
76.
在二维正方形晶格上,将元胞取为4格点正方形,采用3种不同的规则定义块自旋状态,进行了重正化群计算,得出了更为精确的结果;解决了元胞内格点数为偶数的重正化群计算问题. 相似文献
77.
Young C. Kim Mikhail A. Anisimov Jan V. Sengers Erik Luijten 《Journal of statistical physics》2003,110(3-6):591-609
The character of critical behavior in physical systems depends on the range of interactions. In the limit of infinite range of the interactions, systems will exhibit mean-field critical behavior, i.e., critical behavior not affected by fluctuations of the order parameter. If the interaction range is finite, the critical behavior asymptotically close to the critical point is determined by fluctuations and the actual critical behavior depends on the particular universality class. A variety of systems, including fluids and anisotropic ferromagnets, belongs to the three-dimensional Ising universality class. Recent numerical studies of Ising models with different interaction ranges have revealed a spectacular crossover between the asymptotic fluctuation-induced critical behavior and mean-field-type critical behavior. In this work, we compare these numerical results with a crossover Landau model based on renormalization-group matching. For this purpose we consider an application of the crossover Landau model to the three-dimensional Ising model without fitting to any adjustable parameters. The crossover behavior of the critical susceptibility and of the order parameter is analyzed over a broad range (ten orders) of the scaled distance to the critical temperature. The dependence of the coupling constant on the interaction range, governing the crossover critical behavior, is discussed. 相似文献
78.
79.
We study the analytic structure of thermodynamic functions at first-order phase transitions in systems with short-range interactions and in particular in the two-dimensional Ising model. We analyze the nature of the approximation of the d=2 system by anN × strip. Investigation of the structure of the eigenvalues of the transfer matrix in the vicinity of H=0 in the complexH plane allows us to define a new function which provides rapidly convergent approximations to the stable free energyf and its derivatives for allH 0. This new function is used for numerical calculation of the coefficients Cn in the power series expansions of the magnetizationm in the form m(H)=1 + Cn(H-H
0
)n for various H0 0. The resulting series are studied by conventional methods. We confirm recent series analysis results on the existence of the droplet model type essential singularity at H=0. Evidence is found for a spinodal at H=Hsp(Ti < 0. 相似文献
80.
Ross Graham 《Journal of statistical physics》1982,29(2):177-183
We establish the following new correlation inequalities for the truncated twopoint function of an Ising ferromagnet in a positive external field:
j
;
l
T
j
;
k
T
k
;
l
T
, and
j
;
l
T
k K
j
;
k
T
k
l
, whereK is any set of sites which separatesj froml. The inequalities are also valid for the pure phases with zero magnetic field at all temperatures. Above the critical temperature they reduce to known inequalities of Griffiths and Simon, respectively.NSERC Postgraduate Fellow, 1978–1981. Research supported in part by NSF Grant No. PHY-78-25390-A02. 相似文献