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 NdBa₂Cu₃O_7−δ (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 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 B_pk, suggesting that the flux creep mechanism is different below and above B_pk.