Nucleation and hysteresis in Ising model: Classical theory versus computer simulation

We have studied the nucleation in the nearest neighbour ferromagnetic Ising model, in different (d) dimensions, by extensive Monte Carlo simulation using the heat-bath dynamics. The nucleation time (τ) has been studied as a function of the magnetic field (h) for various system sizes in different dimensions (d = 2, 3, 4). The logarithm of the nucleation time is found to be proportional to the power (−(d − 1)) of the magnetic field (h) in d dimensions. The size dependent crossover from coalescence to nucleation regime is observed in all dimensions. The distribution of metastable lifetimes are studied in both the regions. The numerical results are compared and found to be consistent with the classical theoretical predictions. In two dimension, we have also studied the dynamical response to a sinusoidally oscillating magnetic field. The reversal time is studied as a function of the inverse of the coercive field. The applicability of the classical nucleation theory to study the hysteresis and coercivity has been discussed.