Sensitive Single-Level Magnetometers of High Tc dc SQUIDs

We have developed a simple sintering system to prepare the yttria-stabilized-zirconia (YSZ) bicrystals. Grain-boundary junctions made from the epitaxial YBa2Cu3O7-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 1pT/Hz½ at 10 Hz, and increases to 3pT/Hz½ at 1 Hz at 77 K.