Columnar defects and irreversibility lines in Tl-based superconductors

Abstract

Abstract Tl-based superconducting ceramics of different phases (Tl-2212, Tl-1223, Tl-2223) have been irradiated by heavy ions (6 GeV Pb and U). It is shown by high resolution electron microscopy that Pb irradiations induce columnar defects of about the same diameter (95 ± 5) Å in Tl-2223 and Tl-1223 whereas a larger dispersion of the diameter around the value of 95 Å is observed for Tl-2212. The U irradiation leads to diameters slightly more scattered than in the Pb irradiation. These samples have been studied by SQUID magnetometry before and after irradiation. Drastic increases of the critical current induced by the irradiation have been observed and the ‘hierarchy’ existing between phases about the location of their irreversibility lines remains the same after irradiation at the same fluence.