Cotes S M, Albano E V
Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT-La Plata CONICET, La Plata, Argentina.
Phys Rev E Stat Nonlin Soft Matter Phys. 2011 Jun;83(6 Pt 1):061105. doi: 10.1103/PhysRevE.83.061105. Epub 2011 Jun 6.
In this work, we present the results of a systematic exploration of the effect caused by the introduction of nonmagnetic impurities (or defects) on the stabilization of the interface between two magnetic domains of opposite magnetic orientation. Those defects are simulated as spin vacancies along the center of confined two-dimensional Ising films, which have competing magnetic fields acting on the confinement walls. The calculations are performed for different L×M film sizes and by using the standard Metropolis dynamics. In the absence of defects, the film is characterized by an interface running along the M direction, which is induced by the competing surface fields. That interface undergoes a localization-delocalization transition that is the precursor of a true wetting transition taking place in the thermodynamic limit. When the density of defects is relatively low, our results show that the wetting phase transition is of second order, as in the absence of defects. On the other hand, when the density of nonmagnetic impurities is relatively high, a pinning effect of the interface gives rise to a first-order wetting phase transition. The observed transitions are characterized by measuring relevant properties, such as magnetization profiles, cumulants, magnetization fluctuations, etc., as a function of the density of defects. So, our main finding is that the presence of nonmagnetic impurities introduces a rich physical scenery, such as a line of second-order wetting transitions (observed for low density of defects) that merges into a first-order one just at a tricritical point. Precisely, these two latter findings are the major contributions of our study.
在这项工作中，我们展示了对引入非磁性杂质（或缺陷）对具有相反磁取向的两个磁畴之间界面稳定性所产生影响进行系统探索的结果。这些缺陷被模拟为沿受限二维伊辛薄膜中心的自旋空位，在限制壁上存在竞争磁场作用。针对不同的L×M薄膜尺寸并使用标准的 metropolis 动力学进行计算。在没有缺陷的情况下，薄膜的特征是沿着M方向存在一个界面，这是由竞争表面场诱导产生的。该界面经历一个局域化 - 非局域化转变，这是在热力学极限下发生的真正润湿转变的前兆。当缺陷密度相对较低时，我们的结果表明，如同没有缺陷时一样，润湿相变是二级相变。另一方面，当非磁性杂质密度相对较高时，界面的钉扎效应会导致一级润湿相变。通过测量相关性质，如磁化分布、累积量、磁化涨落等作为缺陷密度的函数来表征所观察到的相变。所以，我们的主要发现是，非磁性杂质的存在引入了丰富的物理景象，例如一条二级润湿转变线（在低缺陷密度时观察到），它恰好在一个三临界点处合并为一级转变线。确切地说，后两个发现是我们这项研究的主要贡献。
