超薄膜磁性材料上XY模型的临界现象

Phase transitions of XY model in ultra-thin magnetic film with a triangular lattice

采用经典XY模型 ,阐明了三角格子上层状超薄膜磁性材料的相变和临界现象 .并用Monte Carlo方法对该模型的内部能量、比热、chirality等热力学量进行了计算 .使用finite sizescaling分析法对临界现象的性质进行了论述 .通过上述分析和计算 ,发现该模型在反强磁性层与强磁性层内的chirality在一定范围内随温度的变化急剧增加 ,这是一种新的chirality相变 ;而在另一范围内存在Kosterliz Thouless相变和通常的chirality相变 .这种新的chirality相变的临界系数与系统层数增加无关 ,而通常的chirality相变的临界系数随系统层数增加而增加 .

Phase transitions and critical phenomena have been clarified for an XY model on the triangular lattice of ultra-thin magnetic films. We have calculated the thermodynamic quantities such as the internal energy, the specific heat, the chirality and so on by using Monte-Carlo simulations. The critical behaviours have been clarified by using finite-size scaling analyses. We have found a new critical behaviour due to a steep increase of the chirality as a function of temperature for the XY model on a layered triangular lattice with antiferromagnetic layers and ferromagnetic layers in some range of interaction parameters,. besides the Kosterlize-Thouless transition and the usual chirality transition. In the new chirality transition, the value of a critical exponent has not been observed over any thickness dependence of this value as far as the layered systems are concerned. In the other chirality transition, the value of a critical exponent has been observed over the thickness.