Effects of carbon doping on trapped magnetic field of MgB$_{2}$ bulk prepared by in-situ hot isostatic pressing method

We report the effects of carbon doping on the trapped field properties of MgB $_{2}$ bulks doped with graphite (C) and B $_{4}$ C, which were prepared by an in-situ hot isostatic pressing method. The trapped fields, $B_{\rm T}$ 's were degraded by the graphite and B $_{4}$ C doping above 15 K, which was predominantly due to the lowered $T_{\rm c}$ by the C substitution. However, the slope of $B_{\rm T}(T)$ and the irreversibility line, $B_{\rm irr}(T)$ , determined from the resistive transitions indicated that the $B_{\rm T}$ of the graphite-doped bulk was expected to exceed that of the pristine bulk below 15 K. Contrary to the literature by other groups, B $_{4}$ C did not enhance the vortex pinning properties.