随机横场与晶场作用混合自旋系统的热力学性质

利用有效场理论和切断近似 ,在伊辛模型的框架内考虑随机横场与晶场作用的混合自旋 1 2和自旋 1系统的热力学性质。重点研究了晶场、横场和随机浓度对混合自旋系统相变的影响 ,研究发现在随机横场条件下 ,较小的晶场存在并不能改变临界横场阈值 ;取较大横场值时在某些随机浓度的范围内出现重入相变现象 ,而取较小横场值时则没有出现重入相变现象。给出了有关相图并进行了讨论。

Critical Behavior of the Gaussian Model with Periodic Interactions on Diamond—Type Hierarchical Lattices in External Magnetic Fields

The Gaussian spin model with periodic interactions on the diamond-type hierarchical lattices is constructed by generalizing that with uniform interactions on translationally invariant lattices according to a class of substitution sequences. The Gaussian distribution constants and imposed external magnetic fields are also periodic depending on the periodic characteristic of the interaction bonds. The critical behaviors of this generalized Gaussian model in external magnetic fields are studied by the exact renormalization-group approach and spin rescaling method. The critical points and all the critical exponents are obtained. The critical behaviors are found to be determined by the Gaussian distribution constants and the fractal dimensions of the lattices. When all the Gaussian distribution constants are the same, the dependence of the critical exponents on the dimensions of the lattices is the same as that of the Gaussian model with uniform interactions on translationally invariant lattices.