Magnetic Relaxation and Second Peak of La2-xSrxCuO4 Single Crystals

A second peak in magnetization curve has been observed in La 2-xSrxCuO4 with x = 0.15 and 0.18, while not observed for x = 0. 115. We have evaluated flux pinning energy U eff from magnetic relaxation near the second peak. It was found that U eff showed a maximum at the field less than the field where the second peak observed. The field H efi, where U eff shows a maximum, has been expressed by a relation \(\sqrt {{H_{eff}}} = c(x)(1 - T/{T_c}J)\) . The relaxation behavior in this system cannot be explained from the collective pinning theory. Temperature dependence of the second peak has been compared with that in YBCO. The origin of the second peak is suggested to be different from that in YBCO.