We measured spatial distributions of the trapped magnetic flux density B in polycrystalline YBaCuO superconductors. It is shown that the spatial distribution of B for external magnetic fields is similar to that predicted from the critical state model of the type II superconductor. Furthermore, the spatial gradient of B becomes steep in proportion to the coupling strength among superconducting grains. It is also shown that the spatial distribution of B changes when the grain-coupling strength is degraded by postannealing around 200ºC.
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