Field-induced pinning effect depending on the composition of Nd1+xBa2-xCu3O7-delta single crystals grown by the TSFZ method

We have studied the field-induced pinning effect of Nd1+xBa2-xCu3O7-delta single crystals grown by the TSFZ method using feed rods of Nd1+alphaBa2-alphaCu3O7-delta (alpha = 0 and 0.1). The ICP measurements reveal that Nd, Ba and Cu compositions of both crystals vary along crystal growth direction, The ratios of Ba/Nd in the crystal of alpha = 0.1 are smaller than those of alpha = 0 at every position. The superconducting properties are found to change depending on the variation of compositions in the crystal rod. In the crystal of alpha = 0, weak superconducting regions where Ba2+ is substituted by Nd3+ are supposed to be distributed in the stoichiometric NdBa2Cu3O7-delta matrix and these substituted regions may act as field-induced pinning centers. On the other hand, in the crystal of alpha = 0.1 the field-induced pinning effect is not observed, This is explained by the obscured change in the order parameter at boundaries between the matrix and the substituted regions due to enhanced substitution of Nd3+ for Ba2+.