Flux Pinning and Superconducting Properties of MgB₂-Diamond Nanocomposites

The present investigation focuses on a further performance improvement of disk-shaped bulk MgB₂ superconductors by means of a nanoscopic diamond powder, using a single-step solid-state reaction process. MgB₂ bulks were produced by in-situ solid state reaction in Ar gas using high purity commercial powders of Mg metal and amorphous B mixed in a fixed ratio of Mg:B = 1:2. Further, 0, 0.4, 0.8, and 1.2 wt% of nanoscopic diamond powder was added to improve flux pinning performance of the bulk MgB₂ material. All samples were sintered at 775 °C for 3 hours in Ar atmosphere. X-ray diffraction confirmed that the sample consisted mainly of MgB₂ phase and a small quantity of MgO phase. DC magnetization measurements showed a sharp superconducting transition with onset T_c at around 39.25 K and 37.42 K for the pure and 0.8 wt.% of nanoscopic diamond powder added samples, respectively. The highest self-field critical current density (J _c) around 300 kA/cm² and 105 kA/cm² were recorded at 20 K, in self-field and 1.5 T for the sample with 0.8 wt.% of nanoscopic diamond. The present results show that nanoscopic diamond powder is an effective pinning medium for bulk MgB₂ and might thus be an alternative to further improve the superconducting performance of the bulk MgB₂ material.