THERMALLY ASSISTED FLUX-FLOW IN EPITAXIAL BI2SR2CA2CU3O10-FILMS - ESTIMATION OF THE ANISOTROPY PARAMETER(DELTA THIN)

The thermally activated flux motion in transport-current-carrying epit axial Bi2Sr2Ca2Cu3O10+<delta> thin films was investigated by conventio nal resistive measurements, with the magnetic field B applied parallel to the c-axis and ranging between 10 mT and 3 T. It was found that th e magnetic field and temperature dependence of the activation energy, as well as the form of the irreversibility line in the thermally assis ted flux flow regime, change significantly at a field value B(cr)appro ximate to 0.1 T. This behavior is similar to that reported by us in th e case of Bi2Sr2CaCu2O8+delta thin films, and was interpreted in terms of the occurrence of a dimensional crossover in the vortex system, du e to the increase of the tilt modulus at low fields. We determined an anisotropy factor gamma approximate to 140 for our Bi2Sr2Ca2Cu3O10+del ta films, which is lower than that observed for the Bi2Sr2CaCu2O8+delt a films.