Magnetoresistance of Superconducting Granules and Grain Boundaries in Ceramic YBa2Cu3O7-δ High-Temperature Superconductors in Weak Magnetic Fields

The objective of the work is to establish the contribution of superconductive granules and grain boundaries (weak links) in magnetoresistance rho value of YBa2Cu3O7-delta granular high-temperature superconductor (HTS) at T < T-c. The current-voltage characteristics (CVCs) E(j)(Hext=const) of YBa2Cu3O6.95 ceramic samples were measured in H-ext (0 <= H-ext <=approximate to 500 Oe) magnetic fields. The CVCs E(j)(Htrap=const) of the samples magnetized in H-treat magnetic fields were measured at H-ext = 0. Based on the CVCs, rho(j)(Hext=const), rho(H-ext)(j=const) and rho(j)(Htreat=const) dependences were reestablished. The comparative analysis of rho(j)(Hext=const) and rho(H-ext)(j=const) dependences indicates the magnetic field redistribution between grain boundaries and superconductive granules influence on transport and galvanomagnetic properties of granular HTS. The superconductive grain magnetoresistance rho(g) was established to be significantly lower than rho(J) value of Josephson medium.