HTS dc SQUID behavior in external magnetic fields

Several types of HTS dc SQUID magnetometers - directly coupled magnetometers with either a conventionally solid pickup loop or with 17 narrow loops in parallel and flip-chip magnetometers-are tested concerning their behavior in external fields. The stability against flux penetration was measured by the determination of the magnetic hysteresis. This stability is increased by steep structure edges in the SQUID and in the pickup loop. The intrinsic noise of SQUIDs during operation in external fields was determined by simultaneous measurement of the spectra of two SQUIDs. A directly coupled magnetometer with narrow parallel loops showed much smaller intrinsic noise after movement in the Earth's magnetic field than one with a solid pickup loop.