Godoy Mauricio, Figueiredo Wagner
Departamento de Física--Universidade Federal de Santa Catarina, 88040-900, Florianópolis, Santa Catarina, Brazil.
Phys Rev E Stat Nonlin Soft Matter Phys. 2002 Feb;65(2 Pt 2):026111. doi: 10.1103/PhysRevE.65.026111. Epub 2002 Jan 16.
In this work we investigate the stationary states of a nonequilibrium mixed-spin Ising model on a square lattice. The model system consists of two interpenetrating sublattices of spins sigma=1/2 and S=1, and we take only nearest neighbor interactions between pairs of spins. The system is in contact with a heat bath at temperature T and subject to an external flux of energy. The contact with the heat bath is simulated by single spin flips according to the Metropolis rule, while the input of energy is mimicked by the simultaneous flipping of pairs of neighboring spins. We performed Monte Carlo simulations on this model in order to find its phase diagram in the plane of temperature T versus the competition parameter between one- and two-spin flips, p. The phase diagram of the model exhibits two ordered phases with sublattice magnetizations m(1), m(2)>0 and m(1)>0, m(2)<0. These phases are separated from the paramagnetic phase (m(1)=m(2)=0) by continuous transition lines. We found the static critical exponents along these lines and showed that this nonequilibrium model belongs to the universality class of the two-dimensional equilibrium Ising model.
在这项工作中，我们研究了方形晶格上非平衡混合自旋伊辛模型的稳态。该模型系统由自旋为σ = 1/2和S = 1的两个相互贯穿的子晶格组成，并且我们仅考虑自旋对之间的最近邻相互作用。系统与温度为T的热浴接触，并受到外部能量通量的作用。与热浴的接触通过根据 metropolis 规则的单自旋翻转来模拟，而能量的输入则通过相邻自旋对的同时翻转来模拟。我们对该模型进行了蒙特卡罗模拟，以便在温度T与单自旋和双自旋翻转之间的竞争参数p的平面上找到其相图。该模型的相图展示了两个有序相，其亚晶格磁化强度m(1)、m(2)>0以及m(1)>0、m(2)<0。这些相通过连续的转变线与顺磁相（m(1)=m(2)=0）分隔开。我们沿着这些线找到了静态临界指数，并表明这个非平衡模型属于二维平衡伊辛模型的普适类。
