Investigation on different contributions to the magnetic irreversibility in Bi2Sr2CaCu2O8 single crystals

Hysteresis cycles and relaxation measurements as a function of temperature and field are reported for a very thin Bi2Sr2CaCu20 8 single crystal (thickness =5 I~m). A fishtail effect was observed between 15 and 26 K at a field of = 400 Oe, at which the relaxation rate was found to rapidly increase. The observed behaviour gives evidence of a field-induced 3d-2d dimensional crossover in the vortex lattice in presence of different sources of irreversibility (point and extended planar defects, surface barriers), each of them dominating in different regions of the B-T phase diagram.