Origin and characterisation of peak effect in pure and Pb doped Bi-2212 single crystals

The peak effect in pure and heavily Pb doped Bi2212 single crystals with di fferent oxygen doping levels were studied by measuring M-II loops. The peak effect in pure Bi2212 crystals was obtained only for crystals with optimum oxygen doping and overdoping but not for oxygen underdoping. For Pb-doped Bi2212 crystals, a strong peak effect appeared in higher field than in pure crystals and it persisted up to T-c. Formation and decomposition of Bi5+ a nd/or Pb4+ I ich clusters, which caused the reduction of c-axis and rho (c) , were proposed to be responsible for the appearance and disappearance of t he peak effect In pure and Pb doped crystals. The peak effect was character ised by plotting (H-max-H-min)/H-max vs T/T-c, where H-max and H-min repres ents the field in which the magnetisation reaches maximum and starts to inc rease around secondary peak position, respectively. Results showed that the evolution of the peak effect with temperature in the Pb doped crystals was similar to that in Y123.