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Magnetic hysteresis loops are measured on Bi2Sr2CaCu2O8+δ (Bi-2212) single crystal with different surface states and shapes. The result obtained on Bi-2212 single crystals with dirty and clean surfaces demonstrates that variation of surface state does not result in the disappearance of anomalous magnetization peak H2p and has only an influence on the width of magnetic hysteresis loops. The result obtained on Bi-2212 single crystals with elongated and circular shapes shows that the variation of shape also does not give rise to the disappearance of H2p. The origin of H2p of Bi-2212 single crystal is suggested to originate from other intrinsic reasons and should not be attributed to the surface state and surface shape. [Copyright &y& Elsevier]

Flux pinning and anomalous magnetization peak of heavily overdoped Bi[sub 2-x]Pb[sub x]Sr[sub 2]CaCu[sub 2-y]Cr[sub y]O[sub 8+δ] [Cr-doping (Bi, Pb)-2212] single crystals are investigated by means of magnetization measurements with the magnetic field parallel to the c axis. Compared with undoped Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+δ] (Bi-2212) and Pb-doping Bi[sub 2-x]Pb[sub x]Sr[sub 2]CaCu[sub 2]O[sub 8+δ] [(Bi, Pb)-2212] single crystals, the irreversibility line of Cr-doping (Bi, Pb)-2212 single crystals is pronouncedly shifted to high temperatures. The anomalous magnetization peak H[sub 2p] with maximum peak field near 8000 G is observed. The H[sub 2p] exhibits strong temperature dependence from 0.19 to 0.93T[sub c]. The temperature dependence of H[sub 2p] can be explained according to vortex decoupling theory. The improved flux pinning may originate from reduced anisotropy due to Pb doping and a sufficient number of effective pinning centers due to the random Cr substitution on the Cu site. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Anomalous magnetization is investigated on a heavily Pb-doped Bi2Sr2CaCu2O8+δ as-grown single crystal [(Bi,Pb)-2212] with Tc=92 K. Both the anomalous magnetization peak H2p and the onset of the anomalous magnetization peak Hon are detected in temperature region from 0.3Tc to 0.9Tc based on the descending field branch of magnetic hysteresis loops. At low temperatures below 20 K, the magnetic hysteresis loop behaves as an obvious asymmetry. The double magnetic hysteresis behavior is observed at high temperatures close to Tc. The temperature dependence of H2p can be described according to the thermal disorder induced decoupling theory. The double magnetization behavior may be ascribed to the existence of intra-grain granularity due to the inhomogeneity of oxygen distribution induced by heavily Pb-doping. [Copyright &y& Elsevier]