Zero-temperature dynamic transition in the random field Ising model: a Monte Carlo study

The dynamics of a random (quenched) field Ising model (in two dimensions) at zero temperature in the presence of an additional sinusoidally oscillating homogeneous (in space) magnetic field has been studied by Monte Carlo simulation using the Metropolis single spin flip dynamics. The instantaneous magnetisation is found to be periodic with the same periodicity of the oscillating magnetic field. For very low values of amplitude of oscillating field and the width of randomly quenched magnetic field, the magnetisation oscillates asymmetrically about a nonzero value and the oscillation becomes symmetric about a zero value for higher values of amplitude of oscillating field and the width of the quenched disorder. The time-averaged magnetisation over a full cycle of the oscillating magnetic field defines the dynamic order parameter. This dynamic order parameter is nonzero for very low values of amplitude of oscillating magnetic field and the width of randomly quenched field. A phase boundary line is drawn in the plane formed by the amplitude of the oscillating magnetic field and the width of the randomly quenched magnetic field. A tricritical point has been located, on the phase boundary line, which separates the nature (discontinuous/continuous) of the dynamic transition.