ANOMALOUS MAGNETIZATION BEHAVIOR OF SINGLE CRYSTALLINE BI2SR2CACU2O8+DELTA

Magnetic hysteresis curves as well as reversible magnetization in the superconducting state of single crystalline Bi2Sr2CaCu2O8+delta have been studied. Large hysteresis in magnetization at 4.2 K, which is a manifestation of strong pinning effects, rapidly diminishes around 25 K, where an anomalous peak effect is observed. This peak effect appears sharply in a certain magnetic field at a certain temperature, and is interpreted as a characteristic feature of collective pinning, which is a result of a sudden change of the elastic constant of the flux-line lattice in the vortex state. It is observed that the irreversibility line determined by magnetic hysteresis curves coincides well with the one obtained previously by the temperature dependence of magnetization.