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

Abstract

The objective of the work is to establish the contribution of superconductive granules and grain boundaries (weak links) in magnetoresistance ρ value of YBa2Cu3O7−δ granular high-temperature superconductor (HTS) at T<Tc. The current-voltage characteristics (CVCs) \(E(j)_{H_{\mathrm{ext}} = \mathrm{const}}\) of YBa2Cu3O6.95 ceramic samples were measured in Hext (0≤Hext≤≈500 Oe) magnetic fields. The CVCs \(E(j)_{H_{\mathrm{trap}} = \mathrm{const}}\) of the samples magnetized in Htreat magnetic fields were measured at Hext=0. Based on the CVCs, \(\rho(j)_{H_{\mathrm{ext}} = \mathrm{const}}\), ρ(Hext)j=const and \(\rho(j)_{H_{\mathrm{treat}} = \mathrm{const}}\) dependences were reestablished. The comparative analysis of \(\rho(j)_{H_{\mathrm{ext}} = \mathrm{const}}\) and ρ(Hext)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 ρg was established to be significantly lower than ρJ value of Josephson medium.