Anomalous magnetization characteristics in the overdoped Bi_2-xPb_xSr₂CaCu₂O _8+δ single crystal

Magnetization measurements with the magnetic field parallel to the c-axis were performed on overdoped t_2-xPb_xS₂CaCu₂O_8+δ single crystals. Different from undoped Bi₂Sr₂CaCu₂O_8+δ single crystal, a pronounced anomalous peak with maximum peak field over 5000 G can be observed in enlarging temperature window from 0.2T_c to 0.9T_c; both the anomalous magnetization peak H_2p and the sharp onset of the anomalous magnetization peak H_on exhibit strong temperature dependence up to the vicinity of T_c. The temperature dependence of H_on and H_2p implies that observed anomalous magnetization originates from a static disorder-induced transition from a relatively ordered vortex lattice (or Bragg glass) to a vortex glass (or disordered vortex solid) at H_on and thermal disorder induced pancake vortex decoupling transition at H_2P.