Abstract
Anomalous c-axis isothermal magnetization results are reported for partial Pb-substituted (Bi,Pb) 2 Sr 2 CaCu 2 O 8+δ [(Bi,Pb)-2212] single crystals with overdoped superconducting transition T c of 69 K and anisotropy parameter γ∼39. Contrary to optimum-doped Bi-2212 crystals, both second magnetization peak H 2p (T) and onset field H on exhibit strong and meaningful temperature dependence (150 G-2 kG for H on and 160 G-5.2 kG for H 2p ) in a much extended temperature range from 11 K up to 62 K (0.16∼0.907T c ), where they cross with the low-field irreversibility line H in (T). The theoretical fitting of the temperature variation indicates that H on (T) is related to the static-disorder induced transition from an ordered vortex quasilattice (or Bragg glass) to an entangled vortex glass state, and H 2p (T) seems to be related to the thermal-disorder induced vortex pancake decoupling transition. The H 2p and H on terminations at low and high temperature as well as relaxation are fully discussed. ©2000 The American Physical Society.