Increase in Birr and reduction of anisotropy of MgB2 with Dy2O3/C co-doping

In this study a series of Dy₂O₃/C co-doped MgB₂ bulks and strands were fabricated. The C – doping level was fixed at 2.0 mol% for all the MgB₂ strands. The transport and magnetic properties of MgB₂ strands was systematically investigated in terms of Dy₂O₃ doping level over a wide temperature range. Compared to C-doped-only MgB₂ strand, the Dy₂O₃/C co-doped MgB₂ strands have higher transport J_ct at 4.2 K. The improved transport J_ct – B performance results from the fact that Dy₂O₃ doping can further improve the anisotropy and flux pinning strength of C-doped MgB₂ strand. TEM results of REO doped sample showed nano-size inclusions (20 – 100 nm) present both inside MgB2 grains and on grain boundaries. In-field resistivity measurement (up to 28 T) was performed from 4-40 K. The Bc2 values extracted from both resistivity and magnetic measurements were unchanged by Dy2O3 additives. However, the irreversibility field Bk was increased in response to Dy2O3 doping suggesting a decrease in the anisotropy. The Bk increase, about 1 T between 4-35 K, is of particular interest at higher temperatures (20-30 K).