Influence of lead substitution on the magnetic irreversibility line of 2212 superconducting single crystals

Abstract An experimental study of the magnetic irreversibility lines has been carried out on superconducting single crystals of Bi 2− x Pb x Sr 2 CaCuO 2 O 8 , with and without lead. The irreversibility field values B irr ( T ) are almost identical for x = 0 and x = 0.4. However, the power-law fits of B irr ( T )∼1/ T α at low temperatures provide different exponents α in both cases, α = 6 in the lead-free sample and α = 4 in the lead-substituted sample. At high temperatures a regime change is observed in both samples and B irr vanishes as ( T c − T ) β with β = 1 for x = 0 and β = 0.37 for x = 0.4. A discussion of these results is achieved within the TAFF and vortex solid melting models taking into account a possible “dimensional crossover” of the vortex system behavior.