Sensitive Single-Level Magnetometers of High T_c dc SQUIDS

We have developed a simple sintering system to prepare the yttria-stabilized-zirconia (YSZ) bicrystals. Grain-boundary junctions made from the epitaxial YBa₂Cu₃O_7-δ films on the bicrystal substrates demonstrated Josephson behavior. Using new square washer design, single-level magnetometer of dc superconducting quantum interference. device (SQUID) has been fabricated. Owing to the flux focusing effect of the large washer, the magnetic field sensitivity of the devices has been enhanced. The magnetic field resolution of the magnetometer is IpT/Hz^1/2 at 10Hz, and increases to 3pT/Hz^1/2 at 1Hz at 77K.