Recent Progress of Bulk Magnets Magnetized by Pulsed Field

A MgB₂ superconducting bulk has a promising potential as a quasi-permanent magnet. In this paper, we have performed pulsed-field magnetization (PFM) at T_s = 14-20 K for MgB₂ superconducting bulks with a higher critical current density J_c(B) fabricated by hot isostatic pressing. During PFM, a flux jump frequently took place, and trapped field B_z decreased in the disk-shaped bulks for a higher magnetic field application. However, in the cylindrical bulk with identical J_c(B) characteristics, the flux jump was avoided, and a maximum trapped field of Bz = 0.81 T was obtained at 14 K, which is a record-high trapped field in a MgB₂ bulk by PFM. The electromagnetic and thermal instability was discussed using conventional relations to avoid the flux jump and to enhance the trapped field on the MgB₂ bulks with higher J_c(B), higher thermal conductivity, and lower specific heat.