M ay 1 99 8 Dynamic Magnetization - Reversal Transition in the Ising Model

We report the results of mean field and the Monte Carlo study of the dynamic magnetization-reversal transition in the Ising model, brought about by the application of an external field pulse applied in opposition to the existing order before the application of the pulse. The transition occurs at a temperature T below the static critical temperature Tc without any external field. The transition occurs when the system, perturbed by the external field pulse competing with the existing order, jumps from one minimum of free energy to the other after the withdrawal of the pulse. The parameters controlling the transition are the strength hp and the duration ∆t of the pulse. In the mean field case, approximate analytical expression is obtained for the phase boundary which agrees well with that obtained numerically in the small ∆t and large T limit. The order parameter of the transition has been identified and is observed to vary continuously near the transition. The order parameter exponent β was estimated both for the mean field (β = 1) and the Monte Carlo (β = 0.90 ± 0.02 in two dimension) cases. The transition shows a ”critical slowing-down” type behaviour near the phase boundary with diverging relaxation time. The divergence was found to be logarithmic in the mean field