LOW-NOISE, SINGLE-LAYER YBA2CU3O7-X DC-SQUID MAGNETOMETERS AT 77 K

We describe a low-noise de Superconducting QUantum Interference Device (SQUID) magnetometer that is fabricated from a single layer of YBa2Cu 3O7-x on a 2 cm x 2 cm bicrystal substrate. The magnetometer design co nsists of a single-turn pickup loop that is directly coupled to a low inductance SQUID, Using conventional flux-locked loop electronics with bias current reversal, the white flux noise of several of these magne tometers operated at 77 K is observed to be as law as 2.2 mu Phi(0)/ro ot Hz above 10 kHz, increasing to about 5.7 mu Phi(0)/root Hz at 1 Hz. The field-to-flux conversion efficiency is measured to be 4.6 nT/Phi( 0), resulting in a white magnetic field noise of 10 fT/root Hz above 1 0 kHz, increasing to 26 fT/root Hz at 1 Hz.