Irreversibility and flux creep properties of the superconducting oxide La1.85Sr 0.15CuO4

Torque measurements on a ceramic sample of the oxide La-Sr-Cu-O give information on its superconducting properties. Under steady rotation of the magnetic field torque signals are observed which indicate rigid or viscous responses of the flux line structure depending on the magnetic history of the sample and the strength of the applied field. If the field is turned to a new direction at time zero, the time dependent torque signal displays strong flux creep for fields far below Hc2. The data are discussed in terms of a granular description of the superconductivity. Intrinsic intra-grain flux pinning appears to be weak. Tome 48 N° 11 ’