History Dependence of Weakly Coupled Intergrain Currents in a Sintered Oxide Superconductor
History dependence of the critical current density was measured for a sintered Y-Ba-Cu-O superconductor by resistive and ac inductive methods. The critical current density measured by the two methods took a smaller value in an increasing-field process than in a decreasing one. It was also shown that closed intragrain currents with much larger value were not influenced by the history. This reveals that the history dependence comes only from a weakly coupled intergrain currents. The effect of an excursion of the magnetic field, i.e., addition and removal of a perturbation in the field, on the intergrain current density was examined in detail. A self-field of the closed intragrain currents, which changes its direction depending on the history, is considered to be a cause of the history effect.
KeywordsHistory Effect Critical Current Density Oxide Superconductor History Dependence Bias Magnetic Field
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