Directly coupled direct current superconducting quantum interference device magnetometers based on ramp-edge $Ag:YBa2Cu3O7−x/PrBa2Cu3O7−x/Ag:YBa2Cu3O7−x$ junctions Available to Purchase

Directly coupled dc superconducting quantum interference device (SQUID) magnetometers on $LaAlO3$ substrates were fabricated using ramp-edge superconductor/normal-metal/superconductor junctions, where Ag-doped $YBa2Cu3O7−x$ was used for the electrode and $PrBa2Cu3O7−x$ for the normal-metal barrier. A flux noise of $8×10−6 Φ0 Hz−1/2$ at 10 kHz measured with a dc bias current was achieved at 75 K, which corresponded to a field sensitivity of $400 fTHz−1/2$ for a magnetometer with a pick-up loop area of $8.5 mm×7.5 mm.$ Most significantly, the noise floor increased at lower frequencies with a frequency dependence slightly less than $1/f.$ The field noise of the SQUID magnetometers increased by only 25% after cycling the devices from zero field to 500 mG. In a static earth’s magnetic field background, the field noise of the SQUID magnetometers increased by less than a factor of 2.