Per Arne Rikvold

METASTABLE LIFETIMES IN A KINETIC ISING MODEL : DEPENDENCE ON FIELD AND SYSTEM SIZE

The lifetimes of metastable states in kinetic Ising ferromagnets are studied by droplet theory and Monte Carlo simulation, in order to determine their dependences on applied field and system size. For a wide range of fields, the dominant field dependence is universal for local dynamics and has the form of an exponential in the inverse field, modified by universal and nonuniversal multiplicative power-law prefactors. Quantitative droplet-theory predictions for these dependences are numerically verified, and small deviations from the predictions are shown to depend nonuniversally on the details of the dynamics. We identify four distinct field intervals in which the field dependence and statistical properties of the lifetimes are markedly different. The field marking the crossover between the weak-field regime, in which the decay is dominated by a single droplet, and the intermediate-field regime, in which it is dominated by a finite density of droplets, vanishes logarithmically with system size. As a consequence, the slow decay characteristic of the former regime may be observable in systems that are macroscopic as far as their equilibrium properties are concerned.

Suppressing Roughness of Virtual Times in Parallel Discrete-Event Simulations

In a parallel discrete-event simulation (PDES) scheme, tasks are distributed among processing elements (PEs) whose progress is controlled by a synchronization scheme. For lattice systems with short-range interactions, the progress of the conservative PDES scheme is governed by the Kardar-Parisi-Zhang equation from the theory of nonequilibrium surface growth. Although the simulated (virtual) times of the PEs progress at a nonzero rate, their standard deviation (spread) diverges with the number of PEs, hindering efficient data collection. We show that weak random interactions among the PEs can make this spread nondivergent. The PEs then progress at a nonzero, near-uniform rate without requiring global synchronizations.

Kinetic Ising Model in an Oscillating Field: Finite-Size Scaling at the Dynamic Phase Transition

We study hysteresis for a two-dimensional spin-1/2 nearest-neighbor kinetic Ising ferromagnet in an oscillating field using Monte Carlo simulations. The period-averaged magnetization is the order parameter for a proposed dynamic phase transition (DPT). To quantify the nature of this transition, we present the first finite-size scaling study of the DPT for this model. Evidence of a diverging correlation length is given, and we provide estimates of the transition frequency and the critical indices {beta} , {gamma} , and {nu} . {copyright} {ital 1998} {ital The American Physical Society}

Dynamic phase transition, universality, and finite-size scaling in the two-dimensional kinetic Ising model in an oscillating field

We study the two-dimensional kinetic Ising model below its equilibrium critical temperature, subject to a square-wave oscillating external field. We focus on the multidroplet regime, where the metastable phase decays through nucleation and growth of many droplets of the stable phase. At a critical frequency, the system undergoes a genuine nonequilibrium phase transition, in which the symmetry-broken phase corresponds to an asymmetric stationary limit cycle for the time-dependent magnetization. We investigate the universal aspects of this dynamic phase transition at various temperatures and field amplitudes via large-scale Monte Carlo simulations, employing finite-size scaling techniques adopted from equilibrium critical phenomena. The critical exponents, the fixed-point value of the fourth-order cumulant, and the critical order-parameter distribution all are consistent with the universality class of the two-dimensional equilibrium Ising model. We also study the cross-over from the multidroplet regime to the strong-field regime, where the transition disappears.

Evidence for a dynamic phase transition in [ Co / Pt ] 3 magnetic multilayers

A dynamic phase transition (DPT) with respect to the period

Underpotential deposition of Cu on Au(111) in sulfate-containing electrolytes: A theoretical and experimental study

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Absence of first-order transition and tricritical point in the dynamic phase diagram of a spatially extended bistable system in an oscillating field.

of an applied alternating magnetic field has been observed previously in numerical simulations of magnetic systems. However, experimental evidence for this DPT has thus far been limited to qualitative observations of hysteresis loop collapse in studies of hysteresis-loop area scaling. Here, we present significantly stronger evidence for the experimental observation of this DPT in a

Langevin simulation of thermally activated magnetization reversal in nanoscale pillars

{[\text{Co}(4\text{ }\text{\AA{}})/\text{Pt}(7\text{ }\text{\AA{}})]}_{3}

Three-state lattice gas on a triangular lattice as a model for multicomponent adsorption

-multilayer system with strong perpendicular anisotropy. We applied an out-of-plane time-varying (sawtooth) field to the

D-dimensional interpenetrable-sphere models of random two-phase media: Microstructure and an application to chromatography

{[\text{Co}/\text{Pt}]}_{3}