A direct-coupling-type high-Tc SQUID magnetometer with two pickup loops per SQUID on a substrate has been fabricated. To suppress the flux trapping and vortex entry, the superconducting film of the whole device except a 5-μm-wide transmission-line-shaped SQUID is composed of narrow (5 μm) lines with slots and holes. The threshold field for the flux trapping during field cooling was evaluated to be around 130 μT, a much larger field than the geomagnetic field. Moreover, applying a field after cooling reduced the critical current of the SQUID to zero at 6 μT. And vortex entry into the pickup loop occurred at a field exceeding about 10 μT.
ASJC Scopus subject areas
- Condensed Matter Physics