Mixed state properties of Bi2Sr2Ca2Cu3O10+δ single crystals before and after neutron irradiation

The reversible and irreversible mixed state parameters of Bi2Sr2Ca2Cu3O10+delta (Bi-2223) single crystals were determined by magnetic measurements. One of the samples was exposed to fast neutron radiation in order to investigate the influence of defects introduced into the Bi-2223 matrix. We find that irradiation increases (to a varying extent) the critical current density J(c) over almost the whole field and temperature range analyzed, in particular also at low B. This differs from tapes where a J(c) enhancement was only found at elevated fields. Irradiation also shifted the irreversibility line to higher values and led to an increase in both the magnetic penetration depth lambda(ab) and the upper critical field H-c2. These two parameters have been calculated with the help of a model that takes thermal fluctuations of vortices into account. H-c2, however, would be expected to decrease according to theoretical predictions for d-wave superconductors. The discrepancy is discussed and requires further investigations.