自旋S =1/2具有无规横场的各向异性海森堡模型的相变特性(英文)

The phase transition of spin-1/2 anisotropic Heisenberg model with a random field

运用双自旋集团近似的方法研究了交换作用各向异性和无规场对自旋S =1/2海森堡系统的相变和磁化强度的影响 .当外场为零时存在一个临界交换作用各向异性参数γC.当γ >γC,横向交换作用进一步增强 ,相变温度消失 ,系统处于无序状态 .交换作用各向异性不仅降低了相变温度 。

By use of the two site cluster approximation,we investigate the influence of exchange anisotropy and random field on the phase transition and the magnetization curve in a spin 1/2 Heisenberg system.We find that there is a critical exchange anisotropic parameter γ C=3 293 when B=0.As γ>γ C,the phase transition temperature will disapear and the order state of system will no longer exist.Exchange anisotropic parameter γ not only reduces the phase transition temperature,but also decreases the position of tricritical temperature.