On the irreversibility line in the Chevrel phase superconductors

The field versus temperature phase diagram of the conventional isotropic Chevrel phase superconductor YbMo6S8 determined by DC magnetization measurements shows the existence of an irreversibility line like in the layered high-Tc oxides. This result confirms the data obtained for PbMo6S8 and shows the large influence of thermal fluctuations and disorder on depinning properties of the flux line lattice in these extreme type II superconductors. © 1991.