Aging and memory effects in the nonequilibrium critical behavior of structurally disordered magnetic materials in the course of their evolution from the low-temperature initial state

The Monte Carlo study of the nonequilibrium critical evolution of structurally disordered anisotropic magnetic materials from the low-temperature initial state with the reduced magnetization $m_0=1$ is performed within the broad range of spin densities, $p=1.0$, $0.95$, $0.8$, $0.6$, and $0.5$. It is shown that, in such systems, the pinning of domain walls by structural defects occurring when the evolution starts from the low-temperature state leads to significant changes in the nonequilibrium “aging” and “memory” effects in comparison to those characteristic of the “pure” system. As a result, in the long-term regime at times $t-t_w\gg t_w\gg1$, an anomalously strong slowing down in the correlation effects is revealed. It is shown that a decrease in the autocorrelation function with time occurs according to a power law typical of the critical relaxation of the magnetization in contrast to a usual scaling dependence. Eventually, the limiting value of the fluctuation-dissipation ratio X$^\infty$ for the structurally disordered systems with $p<1$ vanishes, whereas for the pure system, we have X$^\infty=0.784(5)$. The nonequilibrium critical “superaging” stage is found. This stage is characterized by the critical exponent $\mu=2.30(6)$ for weakly disordered systems and by $\mu=2.80(7)$ for the systems with strong disorder.