Depinning dynamics of two-dimensional magnetized colloids on a random substrate

Abstract

We perform Langevin simulations on the depinning dynamics of two-dimensionalmagnetized colloids on a random substrate. On increasing the magnetic field strength, wefind for the first time a crossover from plastic to smectic flows as well as a crossover fromsmectic to elastic crystal flows above depinning. For both the smectic and elastic crystalflows, a power-law scaling relationship could be obtained between the average velocity andapplied driving force. The scaling exponent is found to be larger than 1 for smectic flow.But, for the elastic crystal flow, the scaling exponent is found to be less than1. For the plastic flow, no power-law scaling relationship between the averagevelocity and applied driving force can be derived and history dependence of thedepinning occurs. Within the crossover from plastic to smectic flows, a suddendecrease in the critical driving force is observed, and a sudden increase is foundin the critical driving force across the crossover from smectic to elastic crystalflows, accompanied by a crossing of the curves of average velocity versus drivingforce.