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