DC SQUID magnetometers with the directly coupled pick-up loop

DC SQUID magnetometers with a directly coupled square pick-up loop have been made from single layer YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films using step edge junctions or bicrystal grain boundary junctions on SrTiO/sub 3/ substrates. YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films were deposited by off-axis RF sputtering or laser ablation and patterned by photolithography and Ar ion milling to form the SQUID, pick-up loop and modulation coil. The SQUIDs showed RSJ like current vs. voltage characteristics and voltage modulation in response to external fields at 77 K. The SQUID inductance was 55-140 pH, pick-up loop size was 47 mm/sup 2/ and the effective area of magnetometers estimated from the measured modulation period was 0.2-0.4 mm/sup 2/. The magnetic field noise was 7.4/spl times/10/sup -13/ T//spl radic/(Hz) at 10 Hz and 77 K.<
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