Enhancement of the Meissner effect in single crystals of hysteretic type II superconductors by thermal cycling

The established model, which accounts for the magnetothermal behaviour of isotropic type II superconductors during slow cooling and warming below T c in a static magnetic field, is extended to reproduce the observations of Hyun [Phys. Rev. B 48 (1993) 1244] of the enhancement of the magnitude of the diamagnetic magnetization M g of Nb 3Sn single crystals by thermal cycling between T 1 and T 2, where T 1≪ T 2< T c. The model also predicts that the thermal cycling between chosen T 1 and T 2 will lead to final closed hysteresis loops of M g versus T. The structure of the final hysteresis loops and the corresponding sequences of configurations of magnetic flux prescribed by the model are also described.