The magnetic hysteresis of polycrystalline YBa/sub 2/Cu/sub 3/O/sub x/

The use of polycrystalline YBCO is generally limited by the granularity of the material. To study the magnetic hysteresis due to the granularity of the material, the magnetization curves of polycrystalline YBCO have been measured in fields up to 25 mT and over a range of temperatures, from 4.2 K to just below critical temperature, T/sub c/. In the region where the hysteresis is dominated by flux trapped between grains, the curves have been modeled using a critical state model with a variety of critical state relations J/sub c/(B). Although the model fits individual curves surprisingly well, there are significant discrepancies in the model parameters for curves measured at the same temperature but different fields. >