Godoy Mauricio, Figueiredo Wagner
Departamento de Física-Universidade Federal de Santa Catarina, 88040-900 Florianópolis, SC, Brazil.
Phys Rev E Stat Nonlin Soft Matter Phys. 2002 Sep;66(3 Pt 2A):036131. doi: 10.1103/PhysRevE.66.036131. Epub 2002 Sep 25.
We studied an antiferromagnetic mixed-spin Ising model on the square lattice subject to two competing stochastic processes. 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 the exchange of energy with the heat bath occurs via one-spin flip (Glauber dynamics). Besides, the system interacts with an external agency of energy, which supplies energy to it whenever two nearest neighboring spins are simultaneously flipped. By employing Monte Carlo simulations and a dynamical pair approximation, we found the phase diagram for the stationary states of the model in the plane temperature T versus the competition parameter between one- and two-spin flips p. We observed the appearance of three distinct phases, that are separated by continuous transition lines. We also determined the static critical exponents along these lines and we showed that this nonequilibrium model belongs to the universality class of the two-dimensional equilibrium Ising model.
我们研究了二维正方晶格上的反铁磁混合自旋伊辛模型，该模型受到两个相互竞争的随机过程影响。模型系统由自旋为σ = 1/2和S = 1的两个相互穿插的子晶格组成，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，与热浴的能量交换通过单自旋翻转（格劳伯动力学）发生。此外，系统与一个外部能量源相互作用，每当两个最近邻自旋同时翻转时，该能量源就会向系统提供能量。通过蒙特卡罗模拟和动态对近似，我们得到了模型稳态在温度T与单自旋和双自旋翻转竞争参数p的平面上的相图。我们观察到出现了三个不同的相，它们由连续的转变线分隔。我们还确定了沿这些线的静态临界指数，并表明这个非平衡模型属于二维平衡伊辛模型的普适类。
