TEMPERATURE-DEPENDENCE OF THE MAGNETIC HYSTERESIS OF A YBA2CU3O7-DELTA SINGLE-CRYSTAL

Magnetic hysteresis loops (MHL) have been measured on a single crystal of YBa2Cu3O7-delta using a QD MPMS SQUID magnetometer. The MHLs were recorded in the temperature range 4.4 to 70 K in magnetic fields up to +/- 5 T. A 'fishtail' shape of the MHL was observed at temperatures b etween 10 and 65 K. Position of the fishtail maximum scales well with (1-T/T-c)(1.78) but the corresponding magnetic moment value does not s cale to a single temperature function. The MHL size drops much more ra pidly with increasing temperature at T < 20 K than in the intermediate range (20 to 50 K) where the decrease is proportional to exp(-T/13K). At T > 55 K the character of MHL changes strongly and it seems to bec ome controlled by surface barrier effects.