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 ${\mathit{H}}_{\mathit{c}1}$, we find well-pronounced differences between ZFC and FC magnetizations. At low temperatures, the diamagnetic response of FC samples cooled at ${\mathit{H}}_{\mathit{c}1}$ is reduced due to the polarity changes of many local magnetic moments.