Comparison on Effects of ${\rm B}_{4}{\rm C}$, ${\rm Al}_{2}{\rm O}_{3}$, and SiC Doping on Performance of

Several MgB₂ monofilamentary samples are prepared to evaluate the effects that the doping compounds B₄C, Al₂O₃, and SiC have on critical current density (J_c) and the J_c dependency of magnetic flux density (B) of the sample. All of the samples in this study have Nb sheaths and are manufactured using in situ precursor powders and the Powder-in-Tube fabrication method. The amounts of added impurities are 10 wt.% for B₄C and Al₂O₃, and 3, 10, and 20 wt.% for SiC. A reference sample without any doping is also prepared. All of the samples are heat treated between 650 and 800°C for 30 minutes. The transport J_c(B) characteristics are measured at 4.2 K and the magnetic J_c(B) behavior is obtained in varied temperatures up to 30 K. The changes in connectivity, or effective cross-section, are also evaluated by performing resistivity measurements on the samples after removal of the sheath. Furthermore, the pinning forces of the samples are evaluated from the magnetic measurements.