Temperature dependence of noise properties of directly coupled YBa2Cu3O7 magnetometers with PrBa2Cu3O7 ramp-type Josephson junctions

Abstract Josephson junctions in ramp-type geometry with artificial PrBa 2 Cu 3 O 7 barriers are applied in directly coupled magnetometers. We investigate the noise properties of the magnetometers to optimize for low flux noise. By applying a bias current reversal technique in flux-locked loop noise measurements one can distinguish between flux noise contributions from the Josephson junctions and from the superconducting films. The temperature dependence of the flux noise reveals that critical current fluctuations are the most important noise source at frequencies between 1 Hz and 100 Hz. We reach a level of flux noise of √S Ф (1 Hz - 26μФ 0 /√ Hz at 81 K .