First-order phase transition in a 2D random-field Ising model with conflictingdynamics

Abstract

The effects of locally random magnetic fields are considered in a nonequilibrium Isingmodel defined on a square lattice with nearest-neighbor interactions. In orderto generate the random magnetic fields, we have considered random variables{h} that change randomly with time according to a double-Gaussian probabilitydistribution, which consists of two single-Gaussian distributions, centered at+ho and−ho, with thesame width σ. This distribution is very general and can recover in appropriate limits the bimodaldistribution () and the single-Gaussian one (ho = 0). We performed Monte Carlo simulations in lattices with linear sizes in the rangeL = 32–512. The system exhibits ferromagnetic and paramagnetic steady states. Ourresults suggest the occurrence of first-order phase transitions between theabove-mentioned phases at low temperatures and large random-field intensitiesho for some smallvalues of the width σ. By means of finite size scaling, we estimate the critical exponents in thelow-field region, where we have continuous phase transitions. In addition,we show a sketch of the phase diagram of the model for some values ofσ.