Hysteresis and avalanches in the random anisotropy Ising model - art. no. 134431

The behavior of the random anisotropy Ising model at T = 0 under local rela xation dynamics is studied. The model includes a dominant short-range ferro magnetic interaction and assumes an infinite anisotropy at each site along local anisotropy axes which are randomly aligned. As a consequence, some of the effective interactions become antiferromagneticlike and frustration ap pears. Two different random distributions of anisotropy axes have been stud ied. Both are characterized by a parameter that allows control of the degre e of disorder in the system. By using numerical simulations we analyze the hysteresis loop properties and characterize the statistical distribution of avalanches occurring during the metastable evolution of the system driven by an external field. A disorder-induced critical point is found in which t he hysteresis loop changes from displaying a typical ferromagnetic magnetiz ation jump (large avalanche spanning a macroscopic fraction of the system) to a rather smooth loop exhibiting only tiny avalanches. The critical point is characterized by a set of critical exponents, which are consistent with the universal values proposed from the study of other simpler models.