MAGNETOTRANSPORT BEHAVIOR OF POLYCRYSTALLINE YBA2CU3O7 - A POSSIBLE ROLE FOR SURFACE BARRIERS

The magnetization as a function of external applied magnetic field M(H -ext) of polycrystalline YBa2Cu3O7 (poly-YBCO) exhibits behavior that is more consistent with the geometrical barrier model of Zeldov et al. than that of either the Bean-Livingston surface-barrier model or the Bean critical state strong-pinning model. Correlation of the magnetiza tion measurements with transport measurements suggests that the irreve rsible properties of poly-YBCO, including the critical current density J(c), are dominated by surface-barrier effects. Observation of an inc reasing of J(c) with H-ext at intermediate fields is consistent with a theoretical model that describes the transport behavior in the case o f vortex lattice formation within the superconducting grains that form the Josephson junctions.