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

Abstract

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 Hirr ), upper critical fields (μ 0 Hc 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 Hc 2//ab , Hc 2//c , and Hirr values at 4.2 K. In addition, the critical current density, Jc , increased with Dy2O3 concentration up to 1 wt. % where non-barrier Jc 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 Jc by 40% and 93% compared to 2 and 3 mol. % C doping, respectively. On the other hand, measurements of Tc 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 Hc 2 increase as co-addition). Comparisons to a two-band model for μ 0 Hc 2 in MgB2 allowed us to conclude that the increases in Hc 2//ab , Hc 2//c , and Hirr (as well as concomitant increases in high-field Jc ) 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 Jc of MgB2 at temperatures above 20 K.