Flux pinning by Nd4Ba2Cu2O10 inclusions in NdBa2Cu3O7-δ superconductors:: A combined effect of point, interface, and Δκ pinning at elevated temperatures

We have systematically studied the role of Nd2Ba2Cu2O10 (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 greater than or equal to 77 K): a combination of point and interface pinning in low fields; a combination of interface and Delta kappa pinning in intermediate fields; and interface pinning with st slight influence from Delta kappa 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 Delta kappa pinning.