Local magnetic field distribution in polycrystalline YBa 2 Cu 3 O 7 and its influence on bulk critical currents

The transport critical current density J c has been measured in high quality polycristalline YBa 2 Cu 3 O 7 samples made from extruded preforms. The hysteretic response of J c to applied magnetic fields was studied as a function of temperature (77-87 K) and sample morphology for various field sweeps in the 0-5 KOe range. A variety of samples show a basic J c ∼H −n behavior where n depends on temperature, but is independent of the other variables. A simple model of the local magnetic field distribution is presented and compared to te data, and the theoretical implications of the power law behavior are considered