Flux pinning by Nd₄Ba₂Cu₂O₁₀ inclusions in NdBa₂Cu₃O_7-δ superconductors: A combined effect of point, interface, and Δκ pinning at elevated temperatures

We have systematically studied the role of Nd₄Ba₂Cu₂O₁₀ (Nd422) nonsuperconducting inclusions for flux pinning in oxygen-controlled-melt-growth processed Nd-Ba-Cu-O bulk superconductors. Nd422 inclusions act as interface pinning which is the most dominant in low-field and high-temperature region. In addition, they are also effective in enhancing the critical current density (J_c) even in a high-field region and thus the irreversibility field (B_irr). Three pinning regimes have been identified at elevated temperatures (T≥77 K): a combination of point and interface pinning in low fields; a combination of interface and Δκ pinning in intermediate fields; and interface pinning with a slight influence from Δκ pinning in high fields. Nd422 addition shifted the boundary of the pinning regime to higher fields. We have found overall J_c is almost a simple summation of two contributions: interface pinning and Δκ pinning.