IRREVERSIBILITY TEMPERATURE AND MEISSNER FRACTION IN HIGH-TEMPERATURE SUPERCONDUCTORS

Low field (<30mT) magnetisation measurements have been carried out on BSCCO and YBCO ceramics and on BSCCO single crystals. The Meissner fraction (MF) has been found to obey a power law: MF ∝ Hi-m where Hi is the internal field. The value of m is different for the different samples. The field range over which the power law holds and m increase with temperature. The irreversibility temperature (Ti) determined by a fixed criterion δM, obeys the relation: (Tc-Ti) ∝ Hin. In the case of BSCCO, n increases as δM increases. We argue that present flux pinning models do dot explain these results. © 1990, Elsevier Science Publishers B.V. (North-Holland). All rights reserved.