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arXiv 1304.2525cond-mat.stat-mech
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具有非对称各向异性三峰概率分布的随机场伊辛模型

The random field Ising model with an asymmetric and anisotropic trimodal probability distribution

Ioannis A. Hadjiagapiou

摘要:

研究了由非对称各向异性三峰概率分布$P(h_{i})=p\; δ(h_{i}-h_{0}) + q δ(h_{i}+ λ*h_{0}) + r δ(h_{i})$构成的随机场中的伊辛模型.部分概率$p, q, r$取与约束$p+q+r=1$一致的区间$[0,1]$内的值,不对称分布,$h_{i}$是具有基本绝对值$h_{0}$的随机场变量(强度); $λ$是竞争参数,其是在两个主方向$(+z)$和$(-z)$上的随机磁场的相应强度之间的比率,并且是正的,使得随机场竞争的各向异性分布。这种概率分布是双峰分布的扩展,允许在晶格中存在非磁性颗粒或空位。当前的随机场伊辛系统显示主要是二阶相变,其中,对于某些值的$p, q$和$h_{0}$,其次是一阶相变顺利加入一个三临界点,偶尔,两个三临界点出现暗示另一个二阶相变。除了这些点之外,对于$λ$、$p$和$q$的特定值,在适当的温度和随机场范围内可以看到再入现象。使用变分原理,我们写下的平衡方程的磁化强度和解决它的相变和在三临界点,以确定相对于$h_{0}$的磁化曲线,被认为是一个独立的变量,除了温度。

英文摘要:

The Ising model in the presence of a random field, drawn from the asymmetric and anisotropic trimodal probability distribution $P(h_{i})=p\; δ(h_{i}-h_{0}) + q δ(h_{i}+ λ*h_{0}) + r δ(h_{i})$, is investigated. The partial probabilities $p, q, r$ take on values within the interval $[0,1]$ consistent with the constraint $p+q+r=1$, asymmetric distribution, $h_{i}$ is the random field variable with basic absolute value $h_{0}$ (strength); $λ$ is the competition parameter, which is the ratio between the respective strength of the random magnetic field in the two principal directions $(+z)$ and $(-z)$ and is positive so that the random fields are competing, anisotropic distribution. This probability distribution is an extension of the bimodal one allowing for the existence in the lattice of non magnetic particles or vacant sites. The current random field Ising system displays mainly second order phase transitions, which, for some values of $p, q$ and $h_{0}$, are followed by first order phase transitions joined smoothly by a tricritical point; occasionally, two tricritical points appear implying another second order phase transition. In addition to these points, re-entrant phenomena can be seen for appropriate ranges of the temperature and random field for specific values of $λ$, $p$ and $q$. Using the variational principle, we write down the equilibrium equation for the magnetization and solve it for both phase transitions and at the tricritical point in order to determine the magnetization profile with respect to $h_{0}$, considered as an independent variable in addition to the temperature.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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