Metastable effects and random polarities of magnetic moments in disordered systems of Josephson junctions

We use the Monte Carlo technique to simulate experiments on zero-field-cooled (ZFC) and field-cooled (FC) superconducting samples. As our model we take a three-dimensional, strongly disordered system of Josephson junctions. For fields exceeding a certain critical value Hc1, we find well-pronounced differences between ZFC and FC magnetizations. At low temperatures, the diamagnetic response of FC samples cooled at Hc1 is reduced due to the polarity changes of many local magnetic moments.