Magnetic Flux Invasion and Field-Capturing in Pulsed-Field Magnetization for Layered MgB<formula><tex>$_2$</tex></formula> Bulk Magnets

The pulsed-field magnetization experiments have been carried out for the layered MgB<formula><tex>$_2$</tex></formula> bulk magnets to clarify the magnetic flux motion during the activation processes. Since MgB<formula><tex>$_2$</tex></formula> is characterized as homogeneous, lightweight and inexpensive HTS material in comparison to RE123 compounds (RE=rare earth), the material may have an advantage of possibly uniform magnetic field generation. The values of applied field <formula><tex>$B_a$</tex></formula> which begin to reach the sample center were responsible for the total sample thickness, reflecting the shielding effect to suppress the flux invasion. As well, the estimation on the ratios of trapped field <formula><tex>$B_T$</tex></formula> over penetration field <formula><tex>$B_p$</tex></formula> showed us the reluctant field invasion with increasing sample thickness. The field trapping ratios <formula><tex>$B_{T}B^{p}$</tex></formula> decreased with increasing applied field due to heat generation. In the region over 1.4 T, the drastic flux flow and sudden flux jumps were often observed, which lowered the field-capturing ability. The arriv-ing time which corresponds to the flux increasing speed showed us that the rapid flux invasions which occur in the low-field ranges resulted in the highest field-capturing. This suggests us the possible promotion of field-capturing without significant heat generation.