Magnetic hysteresis of the magnetoresistance and the critical current density in polycrystalline YBa2Cu3O7-δ-Ag superconductors

A systematic study of the magnetic hysteresis in transport properties of polycrystalline YBa2Cu3O7-delta-Ag compounds has been made based on two kinds of measurements at 77 K and under applied magnetic fields up to 30 mT: critical current density J(c)(B-a) and magnetoresistance R(B-a). The R(B-a) curves show a minimum in their decreasing branch occurring at B = B-min which was found to be both the excitation current I,, and the maximum applied magnetic field B-am dependent. In addition, for a certain value of B-am > 5 mT, we have observed that Bmin increases with increasing I-ex and reaches a saturation value. The Jc (B) curves show a maximum in decreasing applied magnetic fields occurring at B = B-max. We have also found that B-max increases with increasing B-am and reaches a saturation value. The minimum in the R(B.) and the maximum in Jc(B) curves were found to be related to the trapped flux within the grains. All the experimental results are discussed within the context of the flux dynamics and transport mechanisms in these high-T-c materials. (C) 2003 Elsevier Science B.V. All rights reserved.