Optimization of processing conditions towards high trapped fields in MgB2 bulks

Abstract

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 250kA/cm2 at 10K and 181kA/cm2 at 20K in self field. We also measured the trapped field values at 20K for bulk MgB2 samples 20mm in diameter and 7mm in thickness, sintered at temperatures in the range of 700–950°C with the same sintering duration of 3h. Almost all the samples exhibited the trapped field values higher than 1T, which shows the high potential of sintered MgB2 bulk materials as trapped field magnets. The highest value of 1.51T at 20K was achieved in the MgB2 sample sintered at 775°C, reflecting its high pinning performance and homogeneous microstructure.