Flux Pinning and Superconducting Properties of MgB₂-Diamond Nanocomposites

Abstract

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 Tc 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 (Jc) 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.