Different roles of anisotropy and disorder on the vortex matter of Bi2Sr2CaCu2O8+δ single crystal

The oxygen doped and Pb-substituted single crystalline Bi2Sr2CaCu2O8+delta samples having T-c,T-on and anisotropy (gamma(2)) ranging respectively from 65 to 93 K and from 773 to 49,715 have been studied in the basis of magneto-resistance and magnetization data. It is found that the lowering of anisotropy due to higher oxygen content or Pb substitution is responsible for the reduction of magnetic field-induced transitional broadening and a shift of H-irr(T) and H-g(T) to higher temperatures and magnetic field. Meanwhile, the increasing disorder manifested by decreasing T-c also leads to the extended range of appearance for the second magnetization peak (SMP) and enlarged critical glassy region. It is shown that decreasing anisotropy does not necessarily lead to the lowering of T-c in contrast to the monotonic dependence of T-c on the disorder measured in the temperature range of SMP effect. Additionally, a remarkable monotonic correlation between T-c and the glassy exponent s has been established. (C) 2002 Elsevier Science B.V. All rights reserved.