Anomalous variation of second magnetization peak and onset field in overdoped single crystals

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