Investigation of magnetic levitation performance of MgB 2 bulks produced by a combination of in-situ and ex-situ approaches

Abstract This study shows that introducing an optimal weight percentage of MgB₂, around 10-20 wt. %, into superconducting samples made from Mg and B mixtures with stoichiometric or Mg-excess compositions maximizes both vertical (Fz) and lateral (Fx) levitation forces. The addition of excess Mg slightly alters peak levitation force magnitudes, but the trends are similar. On the other hand, the presence of extra Mg broadens the optimal doping window, although it is favorable to a higher content of MgO impurity phase. Mechanistically, variations in bulk density, microstructure, critical current density, and pinning force remain minimal across all samples. Conversely, levitation force variations are pronounced, with optimized samples exhibiting a two-fold increase at 20 K in zero-field cooled vertical force, up to  18 N, relative to reference specimens without MgB2-addition of 8-10 N. This divergence implies competing or synergistic microstructural influences alongside dynamic spatial distribution magnetic effects. Notably, high-performance levitation forces are achieved despite low sample densities (54-59 % of the theoretical density of the MgB₂ phase). This combination of low density and high levitation capacity is of much interest considering weight-minimization requirements in mobile and transportation systems.