Integrated high‐Tc multiloop magnetometer

Two integrated, thin‐film multiloop magnetometers (fractional turn SQUIDs) have been fabricated using a YBa2Cu3O7−x‐SrTiO3‐YBa2Cu3O7−x multilayer process. The magnetometers have 16 parallel loops, an outer diameter of 7 mm and effective areas of 1.84 and 1.89 mm2, respectively. The magnetic field noise of the better device, measured in a YBCO tube at 77 K with a bias reversal scheme, was 37 fT Hz−1/2 at 1 Hz and 18 fT Hz−1/2 at 1 kHz.