Development of 4 T Class MgB2 Bulk Magnets Doped by Ti

We have studied the trapped field properties of Ti-doped MgB₂ bulks that were fabricated by a hot isostatic pressing method. The trapped field values of Ti5% doped bulk with 38 mm in diameter and 7 mm in thickness were about 3.6 T at 13.2 K and 2.8 T at 20 K, which were 1.3 times larger than those of the pristine bulk at each temperature. The critical current density was also enhanced by the Ti-doping from 1.7 × 10² A/cm² for the pristine bulk to 3.0 × 10³ A/cm² for the Ti5% doped bulk at 20 K under 4 T. The improvement of the flux pinning properties originated from the TiB₂ thin layer at the periphery of the Ti precipitates, which was acted as a strong pinning center.