Abstract
In this paper, we have reported melanin (C16H2O3N2) as a dopant of MgB2 for the first time. Here, the effects of melanin doping to the microstructures and superconducting properties of bulk MgB2 are thoroughly studied from XRD, SEM, TEM, magnetization, and resistivity data. We have analyzed the critical current density (J (c)), irreversibility field (H (irr)), flux pinning, resistivity, lattice parameters, grain sizes, critical temperatures (T (c)), and other microstructures of all the samples. We have varied the doping percentage according to the nominal atomic ratio of Mg-1.05(B1-x C (x) )(2), x=0,0.02,0.06,0.08,0.1. The J (c) of all the melanin-doped samples are improved as compared to that of the undoped sample in high-field region (above 6 Tesla) at low temperature. The 8 and 10 % doped samples give the best results. The 8 % doped sample registers an enhancement of J (c) by a factor of 3.6 at 7 T and 5 K as compared to that of the undoped one. But, in the low-field region, melanin doping reduces J (c). The H (irr) shows remarkable enhancement at low temperatures below 20 K. The best value of H (irr) was found for the 8 % doped sample. However, H (irr) reduces at high temperatures above 20 K in all the melanin-doped samples. The volume pinning strength of all the doped samples is enhanced over the entire field range. Further improvement in superconducting properties can be achieved by further reducing the size of the melanin particles, increasing density, and improving the homogeneity of doping.