Effects of room-temperature pressure cycling on the critical currents in a YBa2Cu3O7−δ superconductor

Abstract

We have studied the effects of sequential pressure cycling (0–2.8 GPa at room temperature) on the critical currents in a YBa2Cu3O7−δ superconductor. From both low- (0–100 Oe) and high- (up to 5.5 T) field dc magnetic data we identify the contributions to the total critical currents arising from inter- (transport) and intragranular aspects of the superconductor. In our studies, we find that above the pressure limit (≤1.0 GPa) of reversible changes the transport critical current is found to irreversibly decrease by as much as 40%–50% for cycling at 2.8 GPa. However, the intrinsic contribution to the critical current is unaffected. Concomitantly two lower critical fields H*c1 and Hc1 are found necessary to fully characterize the low-field hysteretic loops for these superconductors. One consequence of pressure cycling is that we find H*c1, which signifies the intergranular connectivity, is reduced to lower values. The effects of pressure cycling on the real and imaginary (lossy) components, χ′(T) and χ″(T), of the low-field ac susceptibility are found to be consistent with the dc data.