ANOMALOUS TEMPERATURE-DEPENDENCE OF THE PEAK EFFECT IN IODINE-INTERCALATED BI2SR2CACU2O8-CRYSTALS(Y SINGLE)

Peak effects in the magnetic-field dependence of the magnetization hav e been studied for iodine-intercalated Bi2Sr2CaCu2O8+y (I-BSCCO) singl e crystals. We found that the peak field H-p in I-BSCCO is almost inde pendent of temperature at low temperatures, whereas it shows an anomal ously strong temperature dependence at high temperatures. This contras ts with the behavior of H-p in pure BSCCO where H-p is almost temperat ure independent. The constant value of H, at low temperatures increase s with decreasing anisotropy, which is controlled by the oxygen and io dine contents. This behavior suggests that the dimensional crossover o f vortices is the origin of the peak effect at low temperatures. On th e other hand, the temperature dependence of H, at high temperatures ha s a correlation with the inhomogeneity of the samples. We propose a me chanism for the temperature-dependent peak effect similar to that for the fish-tail effect in YBa2Cu3O7-y.