We describe the magnetic properties expected from a finely divided superconductor—normal-conductor composite. We show that this behavior matches that exhibited by samples of superconducting polysulfur nitride ${\mathrm{}\left(\mathrm{SN}\right)\mathrm{}}_x$. The implications of the composite model for critical-field measurements and for the observation of a decoupling transition are discussed.

• Received 27 July 1981

DOI:https://doi.org/10.1103/PhysRevB.24.6707