Jc– H curves for untwinned orthorhombic YBa 2Cu 3O 7− δ and NdBa 2Cu 3O 7− δ single crystals

Abstract

Critical current density ( J c)– H curves for untwinned orthorhombic YBa 2Cu 3O 7− δ (Y123) and NdBa 2Cu 3O 7− δ (Nd123) single crystals were studied, which were annealed by the heat treatment processes such as two-step heat treatments or continuous cooling heat treatments. These J c– H curves were compared with those for the twinned orthorhombic single crystals. The untwinned orthorhombic single crystals were prepared by two different fabrication processes, which were a detwinning process and a twin-free process. The J c– H curves with H‖ c-axis at and below 70 K for the twinned Y123 single crystals and at and below 85 K for the twinned Nd123 single crystals showed large peak effects. On the other hand, the J c– H curves with H‖ c-axis for the untwinned Y123 and Nd123 single crystals showed quite different tendencies from those for the twinned single crystals. Furthermore, those for the untwinned Y123 and Nd123 single crystals also showed quite different tendencies from each other. Those results proved that the peak effects in the J c– H curves with H‖ c-axis were remarkably affected by the oxygen configurations on Cu–O basal planes for the Y123 single crystals and the Nd/Ba ratio fluctuation for the Nd123 single crystals.