Non-monotonous temperature dependence of the second peak effect in an excessively-oxygen doped Bi2Sr2CaCu2O8+δ single crystal

A study has been carried out on the second peak effect of Bi2Sr2CaCu2O8+δ single crystal with excessive oxygen doping based on its magnetization data. The low temperature (T<30 K) magnetization curve reveals a full valley structure on the temperature dependent curves of both second peak field Hsp(T) and its corresponding onset field Hon(T), in conjunction with the appearance of a much broader temperature range of the peak effect. The high temperature (T>30 K) data are shown to exhibit a transition from ordered to glassy flux line state. The data for Hon(T) in those two temperature regimes have been nicely fitted with corresponding theoretical models for strong disorder induced effects