Abstract
The magnetic relaxation measurements on a heavily Pb-doped Bi <sub>2</sub> Sr <sub>2</sub> CaCu <sub>2</sub> O <sub>8+δ</sub> single crystal were carried out in the vicinity of both the anomalous magnetization peak H <sub>2</sub> p and its onset field H <sub>on</sub> at different temperatures. The results show that both the normalized magnetic relaxation rate S(= -d In M/d In t) and the pinning potential U <sub>0</sub> exhibit remarkable changes near H <sub>on</sub> and H <sub>2p</sub> in the temperature region where H <sub>on</sub> (T) follows the relation of the disorder induced vortex lattice transition, H <sub>on</sub> (T) = H <sub>on</sub> (0)[1 - (T/T <sub>c</sub> ) <sup>4</sup> ] <sup>3/2</sup> . For both H<H <sub>on</sub> and H>H <sub>2p</sub> , S increases and U <sub>0</sub> decreases, respectively, with increasing magnetic fields. A negative power law of U <sub>0</sub> (H)∝H <sup>-α</sup> was observed for both H<H <sub>on</sub> and for H>H <sub>2p</sub> . There exists a minimum in the magnetic-field dependence of S(H) and a maximum in the pinning potential U <sub>0</sub> (H) in the field range between H <sub>on</sub> and H <sub>2p</sub> . At lower temperature region where H <sub>on</sub> (T) deviates from the above relation, U <sub>0</sub> (H) behaves differently. The results are discussed in terms of both collective flux creep model and plastic flux creep model.