SQUID systems for ultra-low-field magnetic resonance (ULF MR) feature superconducting pick-up coils which must tolerate exposure to pulsed fields of up to 100 mT. Using type-II superconductor niobium (Nb) field distortions due to trapped vortices in the wire result. In addition, their rearrangement after quick removal of the pulsed field leads to excess low frequency noise which limits the signal-to-noise ratio. In contrast, type I superconductors, such as lead (Pb), do not exhibit vortices but form an intermediate state with the coexistence of normal and superconducting domains.We measured the magnetization loops of superconducting wire samples of Nb and Pb together with their noise behavior after pulsed fields. Pb also exhibits significant excess low frequency noise once the wire has been driven into the intermediate state.To avoid this problem, we removed the field not abruptly but in a linearly decaying sinusoidal manner thereby degaussing the wire. After application of 57 mT, we found that Nb can be degaussed within at least 50 ms, the shortest time used in this study. Pb can also be degaussed, albeit within 100 ms and a more complex dependency on the degaussing parameters. After successful degaussing, negligible excess low frequency noise is observed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.