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

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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.