A New Cluster Approximation to the Diluted Ising and Heisenberg Ferromagnets
A New Cluster Approximation to the Diluted Ising and Heisenberg Ferromagnets
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稀释伊辛和海森堡铁磁体的新簇近似
DOI：
10.1143/ptp.57.1848
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发表时间：
1977
影响因子：
--
通讯作者：
H. Mano
中科院分区：
文献类型：
--
作者：
H. Mano
本文提出了一种新的团簇近似，使我们能够定量地描述稀释的伊辛和海森堡自旋系统。这种近似是基于通过引入随机变量获得的磁化强度和密度矩阵的集群扩展公式。通过扩大要考虑的集群的大小，它得到了系统的改进。对具有最近邻相互作用的稀磁体系分别采用1、2和3格点近似。Heisenberg模型和Ising模型的居里温度对浓度的依赖关系有很大的不同，而临界浓度的值几乎相同。本文还研究了自旋变量的热平均与其局域环境的关系。
A new cluster approximation which enables us to describe both the diluted Ising and Heisenberg spin systems quantitatively is proposed. This approximation is based upon a cluster expansion formula for the magnetization and density matrices obtained by introducing stochastic variables. It is systematically improved by expanding the size of clusters to be considered. The 1-, 2- and 3-site approximations are applied to the diluted ferromagnets with the nearest-neighbor interaction. Concentration dependence of the Curie temperature for the Heisenberg model is quite different from that for the Ising model, while values of the critical concentration for these two models are almost the same. Dependence of the thermal average of a spin variable on its local environment is also studied.