SELF-ORGANIZED CRITICALITY IN DISORDERED-SYSTEMS

A model of randomly diluted ferromagnets with local random fields exhi biting Barkhausen noise when slowly driven by the external field and a cellular automaton with quenched random bonds are studied by numerica l simulations. The defect cellular automaton maintains critical steady states in the mean-field universality class for all strengths of diso rder and conservative dynamics. In the disordered ferromagnet, the sca ling properties of Barkhausen noise resembling self-organized critical ity are found in the region of moderate disorder with scaling exponent s depending on both the concentration of defect sites and driving rate . The transport properties and the disorder-induced phase transition a re discussed.