Abstract
MgB2 bulk superconductors are expected to be utilized as rare-earth-free and lightweight trapped field magnets. However, the flux jumps frequently happen during the magnetizing processes, and heavily degrade the field-trapping performances. We have investigated the effect of additives to the MgB2 bulk samples prepared by spark plasma sintering process, and observed various flux jumps during the pulsed field magnetizing processes, which were carried out at 14 K which was obtained by the 2-stage GM cryocooler. The authors classified the flux motions as three categories as “no flux flow”, “fast flux flow”, and “flux jump” regions, and investigated the conditions where the flux jumps happen. We observed some drastic flux jumps in the pristine and clarified the effect of graphene addition to the flux jumps. The experimental results showed us a possible expansion of no flux jump region, and suggested us the improvement of field trapping capability.
Highlights
The large-grown high temperature superconducting (HTS) bulk materials are capable of acting as the quasi-permanent magnets in their superconducting state
We focus on the flux-trapping property BT/BP and the occurrence of flux jumps
The flux jumps often occurred in the sample “pure” when the applied field exceeded 1.3 T, and the trapped field drastically decreased to 0.1 T, shown by arrows
Summary
The large-grown high temperature superconducting (HTS) bulk materials are capable of acting as the quasi-permanent magnets in their superconducting state. They are called “trapped field magnets” (TFM) or bulk magnets [1], [2]. High Tc values are not always necessary when we employ cryo-coolers instead of liquid nitrogen. Because we can attain certain low temperature conditions only by turning on the switches of cryo-coolers [3].
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