Mechanism of enhanced critical fields and critical current densities of MgB₂ wires with C/Dy₂O₃ co-additions

A series of monofilamentary powder-in-tube MgB₂ wires were fabricated with 2 mol. % C doping and co-additions of 0-3 wt. % Dy₂O₃. Irreversibility fields (μ ₀ H ), upper critical fields (μ ₀ H ₂), and transport critical currents were measured, and from these quantities, anisotropies $$ and electronic diffusivities $$ were estimated. The addition of 1 wt. % Dy₂O₃ to already optimally C-doped MgB₂ wires produced higher H ₂ , H ₂ , and H values at 4.2 K. In addition, the critical current density, J , increased with Dy₂O₃ concentration up to 1 wt. % where non-barrier J reached 4.35 × 10⁴ A/cm² at 4.2 K, 10 T. At higher temperatures, for example, 20 K and 5 T, co-additions of 2 mol. % C and 2 wt. % Dy₂O₃ improved non-barrier J by 40% and 93% compared to 2 and 3 mol. % C doping, respectively. On the other hand, measurements of T showed that C/Dy₂O₃ co-additions increase interband scattering rates at a lower rate than C doping does (assuming C doping levels giving similar levels of low-T μ ₀ H ₂ increase as co-addition). Comparisons to a two-band model for μ ₀ H ₂ in MgB₂ allowed us to conclude that the increases in H ₂ , H ₂ , and H (as well as concomitant increases in high-field J ) with Dy₂O₃ addition are consistent with increases primarily in intraband scattering. This suggests C/Dy₂O₃ co-addition to be a more promising candidate for improving non-barrier J of MgB₂ at temperatures above 20 K.