Effect of nonsuperconducting secondary inclusions on the magnetization relaxation in melt-processed RBa₂Cu₃O_7-δ (R = Nd and Yb) bulk superconductors at high temperatures

We have studied the effect of nonsuperconducting inclusions on the magnetization relaxation in melt-processed RBa₂Cu₃O_7-δ (R=Nd and Yb) bulk superconductor in a high - temperature region (77≤T ≤90 K). It is found that nonsuperconducting inclusions are mainly effective in reducing the normalized relaxation rate S (≡ -d ln M/d ln t) at low fields [b_irr(≡ μ₀H_a/B_irr)≲0.1] and at high fields (b_irr≳0.4). A suppression in S is observed in an intermediate field region (0.1≲b_irr≲0.4) for the samples exhibiting secondary peak effect, suggesting a relation between the peak and the suppression.