The effects of locally random magnetic fields are considered in a
nonequilibrium Ising model defined on a square lattice with nearest-neighbors
interactions. In order to generate the random magnetic fields, we have
considered random variables {h} that change randomly with time according to
a double-gaussian probability distribution, which consists of two single
gaussian distributions, centered at +ho and −ho, with the same width
σ. This distribution is very general, and can recover in appropriate
limits the bimodal distribution (σ→0) and the single gaussian one
(ho=0). We performed Monte Carlo simulations in lattices with linear sizes in
the range L=32−512. The system exhibits ferromagnetic and paramagnetic
steady states. Our results suggest the occurence of first-order phase
transitions between the above-mentioned phases at low temperatures and large
random-field intensities ho, for some small values of the width σ.
By means of finite size scaling, we estimate the critical exponents in the
low-field region, where we have continuous phase transitions. In addition, we
show a sketch of the phase diagram of the model for some values of σ.Comment: 13 pages, 9 figures, accepted for publication in JSTA