Vacancy effects in an easy-plane Heisenberg model : Reduction of Tc and doubly charged vortices
Vacancy effects in an easy-plane Heisenberg model : Reduction of Tc and doubly charged vortices
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DOI：
10.1103/physrevb.71.094423
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发表时间：
2004-11
影响因子：
3.7
通讯作者：
G. Wysin
中科院分区：
文献类型：
--
作者：
G. Wysin
本文研究了二维磁体中存在低浓度杂质（自旋空位）时热平衡的磁涡旋。一个最近邻海森堡（XXZ）自旋模型与易平面交换各向异性是用来确定静态的热力学性质和涡旋密度通过组合集群和超松弛蒙特卡罗模拟。特别是在低温下，大部分的热生成的涡流成核中心的空缺，在那里他们有一个较低的能量的形成。这一事实是负责减少的涡旋非结合的转变温度随着空位浓度的增加，类似于在平面转子模型中看到的。自旋空位也可能出现具有双拓扑电荷的涡旋（$\ifmmode\pm\else\textpm\fi{} 4\ensuremath {\pi}$面内自旋角的变化），只有当以空位为中心时才稳定。
Magnetic vortices in thermal equilibrium in two-dimensional magnets are studied here in the presence of a low concentration of nonmagnetic impurities (spin vacancies). A nearest-neighbor Heisenberg (XXZ) spin model with easy-plane exchange anisotropy is used to determine static thermodynamic properties and vortex densities via combined cluster and over-relaxation Monte Carlo simulations. Especially at low temperatures, a large fraction of the thermally generated vortices nucleate centered on vacancies, where they have a lower energy of formation. This fact is responsible for the reduction of the vortex-unbinding transition temperature with increasing vacancy concentration, similar to that seen in the planar rotator model. Spin vacancies also present the possibility of the appearance of vortices with double topological charges ($\ifmmode\pm\else\textpm\fi{}4\ensuremath{\pi}$ change in in-plane spin angle), stable only when centered on vacancies.