Pinning in Nd-based 123-superconductors

By means of a scaling analysis of the volume pinning forces, Fp, normalized by the maximum value, Fp,max, versus the reduced field h = H a /H irr where H irr denotes the irreversibility field, we analyze the pinning properties of various Nd-based superconductors of the 123-type. NdBa2Cu3O7-δ (NdBCO) samples show a peak in the scaled Fp-graphs above 0.4, and the ternary compounds (Nd0.33Eu0.33Gd0.33)Ba2Cu3Oy (NEG) even at ≈0.5. This high peak position provides strong evidence for a dominant pinning caused by spatial variations of the transition temperature, T c , throughout the samples. In NdBCO single crystals, two peaks are observed in the magnetization loops. Angular dependent measurements clarified that this extra peak is due to twin plane pinning.