Pulse-Field Magnetization for Disc-Shaped MgB₂ Bulk Magnets

MgB₂ bulk magnets are one of the attractive bulk superconductors because they have homogeneous trapped field distribution, low material costs, lightweight, and so on. Pulse-field magnetization (PFM) also has some effective advantages in the point of view of compact setup, shorter magnetizing time, and an inexpensive way to magnetize the bulk samples. However, the trapped field by PFM is inferior to those by field cooling magnetization due to the heat generation caused by sudden changes of the magnetic flux motion. Especially, the temperature rise is remarkable for MgB₂ bulk magnets because of its low specific heat. In this study, we have carried out the PFM technique for five-stacked or three-stacked MgB₂ bulk samples to analyze the flux-invasion behavior. These samples were fabricated by ball-milling and hot-pressing. As a result, maximum trapped field of B_T = 0.64 T was obtained at 14.6 K at the center of the topmost sample when the external magnetic field B_ex of 0.90 T was applied. As B_ex increases further, B_T were dramatically decreased because of heat generation. Furthermore, flux jumps frequently took place in the applied field higher than 2.0 T.