Systematics of transport critical-current-density hysteresis in polycrystalline Y-Ba-Cu-O

We have characterized the dependence of the transport critical current density of the polycrystalline ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{x}}$ superconductors on magnetic field and temperature history as a function of the applied field. Large hysteretic enhancements in the critical current density are observed upon changing the field direction. The enhancements are a strong function of the maximum applied field. Further, a novel field dependence of the critical current density is observed in field-cooled samples. The results indicate that currents circulating within the grains strongly influence the transport current.