Effect of a static magnetic field on a slotted high-T-c SQUID magnetometerwithout a flux dam

A direct-coupling-type high-critical-temperature (high-T-c) SQUID magnetome ter with two pickup loops per SQUID on a bicrystal substrate has been fabri cated. To avoid flux trapping, the superconducting films of the pickup loop s have slits with a separation of 5 mum To suppress flux entry into the pic kup loops, there are no weak links on the pickup loops, ie., no flux dams, In field Fooling, noise did not substantially increase in low frequency reg ion unless the Field reached around 100 muT Regardless of whether the magne tometer was previously zero-field-cooled or field-cooled, the flux did not enter the pickup loop until the changing field exceeded about 10 muT The ma gnetometer cooled under the geomagnetic- and environmental-field noise coul d work in an unshielded environment. A gradiometer was made by connecting t he feedback coils of two magnetometers in series. The environmental field n oise was reduced by the gradiometer by about 35 dB,