  We present a numerical and theoretical study that supports and explains
recent experimental results on anomalous magnetization fluctuations of a
uniaxial ferromagnetic film in its low-temperature phase, which is forced by an
oscillating field above the critical period of the associated dynamic phase
transition (DPT) [P. Riego, P. Vavassori, A. Berger, Phys. Rev. Lett. 118,
117202 (2017)]. For this purpose, we perform kinetic Monte Carlo simulations of
a two-dimensional Ising model with nearest-neighbor ferromagnetic interactions
in the presence of a sinusoidally oscillating field, to which is added a
constant bias field. We study a large range of system sizes and supercritical
periods and analyze the data using a droplet-theoretical description of
magnetization switching. We find that the period-averaged magnetization, which
plays the role of the order parameter for the DPT, presents large fluctuations
that give rise to well-defined peaks in its scaled variance and its
susceptibility with respect to the bias field. The peaks are symmetric with
respect to zero bias and located at values of the bias field that increase
toward the field amplitude as an inverse logarithm of the field oscillation
period. Our results indicate that this effect is independent of the system size
for large systems, ruling out critical behavior associated with a phase
transition. Rather, it is a stochastic-resonance phenomenon that has no
counterpart in the corresponding thermodynamic phase transition, providing a
reminder that the equivalence of the DPT to an equilibrium phase transition is
limited to the critical region near the critical period and zero bias.
