MAGNETIC-RELAXATION, LOWER CRITICAL-FIELD AND IRREVERSIBILITY LINE OFW-DOPED (BI,PB)-2223 SUPERCONDUCTOR

We report magnetic relaxation, lower critical field and irreversibilit y line studies of a single phase W doped (Bi,Pb)-2223 superconductor. The temperature dependence of remanent magnetization exhibited a rapid drop at T less than or equal to 20 K and was due to the drastic decre ase of critical current density (J(c)). The activation energy U-0 dete rmined from magnetic relaxation measurements showed that there exists two types of pinning centres in the vortex lattice. The temperature de pendence of lower critical field (H-c1) exhibited a kink around 25 K. Possible reasons for exhibited anomaly in H-c1 were discussed. The irr eversibility line exhibited an exponential decrease with increasing te mperature and is due to the existence of break down field of proximity effect, induced superconductivity in layered HTSC. Fermi velocity in superconductivity regions (V-FN) is found to be a factor of ten larger than that in normal regions (V-FN).