Double anomalies in heat capacity and dc and ac magnetization in a superconducting Pb-porous glass nanocomposite

Studies of ac and dc magnetization and heat capacity in a superconducting lead-porous glass nanocomposite were carried out. Double anomalies were found on their temperature dependences at different magnetic field. The positions of anomalies of heat capacity and ac and dc magnetization correlated with each other. The additional, low-temperature anomalies shifted remarkably with increasing magnetic field. The FC and FCW curves observed upon cooling and warming, respectively, showed thermal hysteresis at the second step. The peak effect on magnetization loops was seen above 6 K. The low-temperature anomalies in the ac and dc magnetization were treated as a manifestation of transformation in the vortex system which is triggered by superconductivity in confined lead islands.