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 cha racteristics of NdBa2Cu3O7-delta (Nd123) crystals. Like Y2BaCuO5 parti cles in the Y-Ba-Cu-O system, the addition of Nd422 could enhance crit ical current density J(c) at lower fields. The peak field (B-pk) and t he J(c) value at B-pk were almost independent of Nd422 contents althou gh a slight decrease in J(c) at B-pk was observed with increasing Nd42 2 contents. The normalized relaxation rate (S) increased for all the s amples when the field exceeded B-pk The addition of Nd422 was effectiv e in preventing a rapid increase in S above B-pk The exponent mu, defi ned in the collective creep model, was deduced by fitting the experime ntal 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 E lsevier Science Ltd. All rights reserved.