UNIVERSALITY OF MAGNETIZATION CURVES IN SUPERCONDUCTING BI-SR-CA-CU-O AND Y-BA-CU-O FILMS

Magnetization measurements have been performed on c-axis oriented films of Bi2Sr2CaCu2O8 and YBa2Cu3O7-delta in wide ranges of the temperature T and magnetic field H. For fields along the c-axis, we found a universal relation between the reduced quantity of magnetization hysteresis m = DELTA-M/DELTA-M0 and the reduced field h = H/H*, where DELTA-M0 is the hysteresis of magnetization DELTA-M at H = 0 and H* is the irreversibility field. The relation is practically independent of temperature and materials investigated. The hysteresis m decreases exponentially with increasing h except h approximately 1, while the field dependence deviates from the exponential decay for h approximately 1 and m = 0 at h = 1. This dependence of m can be interpreted within the framework of the flux creep model in which the logarithmic current dependence at high current density and the linear current dependence at low density are assumed for the effective pinning potential.