Stochastic nature of the ultrasharp metamagnetic jumps in Dy-Fe-Ga-based intermetallic alloys

DyFe₃ is a know ferrimagnetic material with Dy and Fe sublattices remaining antiparallel to each other. We created a disorder at the Fe sublattice by doping a small amount of nonmagnetic Ga. The resulting alloys (DyFe_3-xGa_x, x = 0.5,1) show spectacular step-like discontinuous jumps in the magnetization versus temperature isotherm at 2 K. The jumps are of different heights, and they are innumerable in number. The number of jumps is found to be higher in the case of x = 0.5 sample compared to that of x = 1. These multiple jumps vanish as we increase the temperature above 4 K. The profile of the jumps follows a certain pattern, but the critical fields for the jumps are random. The height distribution of the jumps follows a power law indicating a scale-invariant nature of the jumps. The jumps also do not show any temporal effect, i.e., they do not occur spontaneously even when one waits for a long time slightly below a metamagnetic field. The magnetization does not show significant relaxation, and the jumps do not show any systematic change with the sweep rate of the external driving field. To understand the origin of the jumps, we have formulated a two-dimensional random bond Ising type spin system. Our computational work based on classical Monte Carlo simulation can qualitatively reproduce the jumps and their scale-invariant character. It indicates that the disorder due to the random occupancy of Ga at the Fe site plays an important role, and it is instrumental in the formation of antiferromagnetically coupled Dy and Fe clusters of finite size. The flipping of Dy and Fe clusters is responsible for the observed discrete avalanche-like features in the hysteresis loop. The present phenomenon can be well described within the realm of self-organized criticality.