DC SQUID MAGNETOMETERS FROM SINGLE LAYERS OF YBA2CU3O7-X

We have fabricated magnetometers patterned in a single layer of YBa2Cu 3O7-x involving dc superconducting quantum interference devices (SQUID s) with bicrystalline grain boundary junctions. The magnetometers cons ist of either a SQUID with a large area square washer or a single turn pickup loop coupled directly to the body of a small area SQUID. We fo und that the transfer function falls off with increasing SQUID inducta nce much more rapidly than predicted; implications for magnetometer pe rformance are discussed. When operated at 77 K with a bias reversal te chnique a directly coupled magnetometer had a noise of (105 +/- 10) fT Hz -1/2 at 1 kHz, increasing to (145 +/- 10) fT Hz -1/2 at 1 Hz.