The nanometer-scale correlated pinning disorder filling channels between regular twin boundaries in the melt-textured (Nd,Eu,Gd)Ba2Cu 3Oy composite is studied. Aligned with regular twin boundaries but tightly packed on nm-scale, this pinning medium is capable to significantly enhance pinning performance at high magnetic fields. We show that oxygen annealing plays a principal role in the formation mechanism of this defect type. It seems that the nanoscale lamelar structure is extremely sensitive to the oxygenation procedure and to the terminal temperature.
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