Influence of Sr doping on the second magnetization peak and the critical current density of YBa 2Cu 3O 7− δ single crystals

Abstract

Magnetic hystheresis loops of a series of YBa 2− x Sr x Cu 3O 7− δ ( x=0.1, 0.25, 0.37 and 0.5) single crystals reveal a huge “peak effect” over a wide range of low temperatures. Previous magnetoresistivity and magnetic irreversibility measurements already have evidenced that the superconducting state of these samples has a granular character and that their magnetic irreversibility line crosses over from the high field flux-creep (fc) regime to low field regimes, characterized by the intergrain Josephson flux-dynamics in a frustrated superconducting-grain aggregate. The present work adds to this that the peak effect vanishes at the temperature limit where the crossover from the fc to the low field regimes takes place. This is a clear indication that the peak effect is entirely related to the intragrain Abrikosov flux-dynamics.