Papers by Author: Pavel V. Prudnikov

Abstract: The Monte-Carlo study deals with ultrathin magnetic films critical behavior. Uniaxial anisotropy, long-range dipolar interactions and external magnetic field competition effects on phase transition, domain structure and system properties were investigated. Striped spin configurations are demonstrated for system with strong dipolar interaction. The effective antiferromagnetic character of dipolar interaction is observed in bilayer structure. Memory effects in non-equilibrium critical time relaxation of magnetization and autocorrelation function are investigated.

Abstract: The Monte Carlo description of aging properties in nonequilibrium critical behaviour of 3D site-diluted Ising model is considered with evolution from ordered initial state with wide range of spin concentrations. At first, it was shown, that pinning of domain walls on defects leeds to a sharp change of aging properties in diluted systems in comparison with pure system. Therefore, the asymptotic value of the fluctuation-dissipative relation becomes equal to null for diluted systems, while for pure system = 0.784(5).

Abstract: The simultaneous effect of non-equilibrium initial states and correlation betweendefects of the structure on the evolution of anisotropic disordered systems at the critical pointwas analyzed. The field theory description of the non-equilibrium critical behavior of three-dimensional disordered systems with the long-range correlated defects was given and the dy-namical critical exponent of the short-time evolution was calculated in the two-loop approxima-tion without the use of the "-expansion. The values of the dynamical critical exponent obtainedby using various methods for summing asymptotic series were compared with the results ofthe computer simulation of the non-equilibrium critical behavior of the three-dimensional dis-ordered Ising model in the short-time regime.

Abstract: Renormalization-group approach is applied to investigate the short-time nonequilibriumcritical behavior of pure and diluted spin systems with nonmagnetic point-like impurities.The dissipative relaxation dynamics with non-conserved order parameter is considered. For thefirst time the description of the order parameter growth induced by the initial nonequilibriumstate of system is carried out at fixed dimension d = 3 without use of ε-expansion.

Abstract: The dynamic critical behavior of the three-dimensional Heisenberg model with longrangecorrelated disorder was studied by using short-time Monte Carlo simulations at criticality.The static and dynamic critical exponents are determined. The simulation was performed fromordered initial state. The obtained values of the exponents are in a good agreement with resultsof the field-theoretic description of the critical behavior of this model in the two-loopapproximation.

Abstract: The ageing phenomena in two-dimensional XY model at the low temperatures are investigated by Monte-Carlo method. The two-time correlation function and dynamic susceptibility are measured. Violations of the fluctuation-dissipation theorem are investigated.