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 MgB2 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 (Jc) 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 MgB2 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.