Dynamic transitions in pure Ising magnets under pulsed and oscillating fields

Abstract

Responses of pure Ising systems to time-dependent external magnetic fields, like pulsed and oscillating fields, are discussed and compared here. Because of the two time scales involved, namely the thermodynamic relaxation time of the system and the pulse width or the time period of the external field, dynamically broken symmetric phases appear spontaneously when both become comparable. A particularly simple case is that of an Ising ferromagnet below its static critical temperature, when it is perturbed for a short duration by a pulsed magnetic field competing with the existing order in the system. If the field strength and duration is more than the threshold (dependent on the temperature), the system, and consequently the magnetization, switches from one minimum to the other of the static free energy. This magnetization reversal transition here shows intriguing dynamic transition behaviour, similar to that for oscillating fields. Monte Carlo studies for such dynamic transitions are discussed and compared with the mean field results for the same and the Monte Carlo results for the oscillating field case. In particular, we discuss the Monte Carlo results for the fluctuations and their growth behaviour near this magnetization reversal (dynamic) transition point.