Fractal description of ferromagnetic glasses and random Josephson networks

Abstract

The well-known analogies between X-Y ferromagnets and superconducting junction arrays are discussed in the light of data on critical exponents of the latter. The role of disorder is analysed. It is shown that, although the Harris criterion seemingly predicts that disorder is irrelevant, its application to fractal percolating clusters predicts exponent values in very good agreement with experiment.