Effect of Nd4Ba2Cu2O10 addition on the pinning properties of Nd-Ba-Cu-O crystals

We have studied the effects of Nd4Ba2Cu2O10 (Nd422) on the pinning characteristics of NdBa2Cu3O7-delta (Nd123) crystals. Like Y2BaCuO5 particles in the Y-Ba-Cu-O system, the addition of Nd422 could enhance critical current density J(c) at lower fields. The peak field (B-pk) and the J(c) value at B-pk were almost independent of Nd422 contents although a slight decrease in J(c) at B-pk was observed with increasing Nd422 contents. The normalized relaxation rate (S) increased for all the samples when the field exceeded B-pk The addition of Nd422 was effective in preventing a rapid increase in S above B-pk The exponent mu, defined in the collective creep model, was deduced by fitting the experimental data and was found to show strong field dependence. We found that mu changes from positive to negative at around B-pk, suggesting that the flux creep mechanism is different below and above B-pk. (C) 1998 Elsevier Science Ltd. All rights reserved.