Flux pinning energy of YBa 1.9Na 0.1Cu 3O 7− δ

Abstract

Na-doped YBa 1.9Na 0.1Cu 3O y +40 mol%Y211 (YBNCO) and Na-free YBa 2Cu 3O y (YBCO) samples were fabricated by the melt-textured growth (MTG) method to study the effect of doped Na ion on flux pinning. The effective pinning energy ( U( T, H dc, J)), irreversibility line ( H irr( T)) and critical current density ( j c( H dc)), were determined by measurement of ac susceptibility (acs) as well as hysteresis loop measurements for the samples, where T, H dc and J are temperature, dc magnetic field and current density, respectively. It is found that H irr( T) was shifted to lower temperatures while J c( H dc) and U( T, H dc, J) of YBNCO became smaller than that of YBCO. Hence, the doping Na ion plays a negative rule on enhancing flux pinning in YBCO. The appearance of the second peak in J c( H dc) relation and the enhancement of anisotropy in YBNCO is a further support to the conclusion.