Anomalous variation of second magnetization peak and onset field in overdoped (Bi,Pb)(2)Sr2CaCu2O8+delta single crystals

Anomalous c-axis isothermal magnetization results are reported for partial Pb-substituted (Bi,Pb)(2)Sr2CaCu2O8+delta [(Bi,Pb)-2212] single crystals wi th overdoped superconducting transition T-c of 69 K and anisotropy paramete r gamma similar to 39. Contrary to optimum-doped Bi-2212 crystals, both sec ond magnetization peak H-2p(T) and onset field H-on exhibit strong and mean ingful temperature dependence (150 G-2 kG for H-on and 160 G-5.2 kG for H-2 p) in a much extended temperature range from 11 K up to 62 K (0.16 similar to 0.90T(c)), where they cross with the low-field irreversibility line H-ir r(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, a nd H-2p(T) seems to be related to the thermal-disorder induced vortex panca ke decoupling transition. The H-2p and H-on terminations at low and high te mperature as well as relaxation are fully discussed.