Magnetoresistance of Superconducting Granules and Grain Boundaries in Ceramic YBa_2Cu_3O_(7-δ) High-Temperature Superconductors in Weak Magnetic Fields

摘要

The objective of the work is to establish the contribution of superconductive granules and grain boundaries (weak links) in magnetoresistance p value of YBa_2Cu_3O_(7-δ) granular high-temperature superconductor (HTS) at T < T_c. The current-voltage characteristics (CVCs) E(j)_(H_(cx1)=const) of YBa_2Cu_3O_(6.95) ceramic samples were measured in H_(ext) (0 ≤ H_(ext) ≤≈ 500 Oe) magnetic fields. The CVCs E(j)_(H_(trap)=const) of the samples magnetized in H_(treat) magnetic fields were measured at H_(ext) = 0. Based on the CVCs, ρ(j)_(H_(ext)=const), ρ(H_(ext))_(j=const) and ρ(j)_(H_(treat)=const) dependences were reestablished. The comparative analysis of ρ(j)_(H_(ext)=const) and ρ(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 ρ_g was established to be significantly lower than ρ_J value of Josephson medium.