Pulsed field magnetization of a 36 mm diameter single-domain Sm-Ba-Cu-O bulk superconductor at 30, 35 and 77 K

A c-axis oriented single-domain Sm-Ba-Cu-O bulk superconductor 36 mm in diameter was magnetized by the pulsed field magnetization (PFM) method at 30, 35 and 77 K. The trapped field distributions after applying pulsed fields with different amplitudes were measured by scanning a Hall sensor 0.5 mm above the surface of the sample. We also measured the time evolution of magnetic fields during the PFM by using an oscilloscope connected to two Hall sensors mounted on the bulk superconductor surface. Fluxes are found to penetrate into the bulk superconductor and to escape from it by choosing passes through the direction inclined at 45° to growth sector boundaries (GSBs) of the sample. At 35 K, the temperature rise of the sample caused by heat generation due to flux motion becomes more substantial than that at 77 K. Thus, flux jumps occurred through the passes and assisted magnetic fluxes to reach rather easily the centre of the bulk superconductor. As a result, the magnetic field necessary for PFM is lower than that to fully magnetize the sample by means of the static zero-field-cooling magnetization method. The optimized multi-PFM with reducing amplitudes, which was specifically referred to as the IMRA technique, turned out to be very effective in achieving excellent trapped field characteristics by PFM at low temperatures. We could achieve a maximum trapped field of 3.6 T together with a well conical trapped field distribution at 30 K.