Monte Carlo investigations of the influence of structural defects on aging effects and the violation of the fluctuation-
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DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Monte Carlo Investigations of the Influence of Structural Defects on Aging Effects and the Violation of the Fluctuation–Dissipation Theorem for a Nonequilibrium Critical Behavior in the ThreeDimensional Ising Model V. V. Prudnikov*, P. V. Prudnikov**, and E. A. Pospelov Omsk State University named after F.M. Dostoevsky, pr. Mira 55a, Omsk, 644077 Russia * email: [email protected] ** email: [email protected] Received June 15, 2013
Abstract—The specific features of a nonequilibrium critical behavior in the threedimensional structurally disordered Ising model have been studied numerically by the Monte Carlo method. An analysis of the two time dependence of the autocorrelation function and the dynamic susceptibility for systems with spin con centrations p = 0.8 and 0.6 has revealed the aging effects, which are characterized by a slowing down of the relaxation of the system with an increase in the waiting time, and the violation of the fluctuation–dissipation theorem. The values of the universal limit of fluctuation–dissipation ratio for the considered systems have been obtained using the Monte Carlo method. It has been shown that the presence of structural defects in the system leads to an enhancement of the aging effects and to an increase of the values of the limit of fluctua tion–dissipation ratio. DOI: 10.1134/S1063776114020204
1. INTRODUCTION In recent years, investigation of the systems charac terized by a slow dynamics has attracted considerable interest from both the theoretical and experimental points of view [1–4]. This is associated with the aging properties, which are predicted and observed during a slow evolution of the systems from a nonequilibrium initial state and characterized by violations of the fluc tuation–dissipation theorem. Wellknown examples of these systems with slow dynamics and aging effects are complex disordered structures, such as spin glasses [5– 7]. At the same time, these features of the nonequilib rium behavior, as was shown by analytical and numeri cal studies [8–10], can be observed in ferromagnetic systems in the vicinity of the secondorder phase transi tion point, because their critical dynamics is character ized by anomalously long relaxation times. It should be noted that the fluctuation–dissipation ratio previously introduced for spin glasses, which relates the twotime spin response function to the twotime correlation function and generalizes the fluctuation–dissipation theorem to the case of a nonequilibrium behavior, becomes a new universal characteristic for the critical behavior of various systems [8]. In this work, we have solved the problem of Monte Carlo numerical investigation of the specific features in the influence of quenched point defects of the struc ture on the characteristics of a nonequilibrium critical behavior of threedimensional spin systems described
by the Ising model. It should be noted that the univer sality class of the critical behavior of a threedimen sional Ising
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