Optimization of processing conditions towards high trapped fields in MgB₂ bulks

The present investigation focuses on the effects of various sintering temperatures on the critical current densities and the trapped field values of disk-shaped bulk MgB₂ superconductors fabricated with a simple solid state reaction. The samples were prepared by varying the sintering temperature from 750 to 950 °C in pure Ar atmosphere. Scanning electron microscopy (SEM) and X-ray diffraction analyses showed that single phase and homogenous MgB ₂ bulks are produced in using sintering temperatures in the range of 750-825 °C. The samples sintered at 775 °C showed the highest critical current density (J_c) values of 250 kA/cm² at 10 K and 181 kA/cm² at 20 K in self field. We also measured the trapped field values at 20 K for bulk MgB₂ samples 20 mm in diameter and 7 mm in thickness, sintered at temperatures in the range of 700-950 °C with the same sintering duration of 3 h. Almost all the samples exhibited the trapped field values higher than 1 T, which shows the high potential of sintered MgB ₂ bulk materials as trapped field magnets. The highest value of 1.51 T at 20 K was achieved in the MgB₂ sample sintered at 775 °C, reflecting its high pinning performance and homogeneous microstructure.