Determination of the robustness of an HTS SQUID magnetometer covered with a superconducting film shield in an ac magnetic field

Abstract

A simple flip-chip configuration of YBa2Cu3O7−x (YBCO) square and cross-shaped films overlapping on a directly coupled multi-pickup-loop HTS dc-SQUID magnetometer was tested to enhance the robustness of the HTS SQUID magnetometer in an ac magnetic field. The YBCO films were expected to work as a superconducting shield to prevent flux vortices from entering and moving in the device. With the shields, most of the SQUID's characteristics such as critical current Ic, modulation voltage Vpp, magnetic flux noise Sϕ1/2, effective area Aeff, and magnetic field noise SB1/2 were enhanced. The robustness of the magnetometer in an applied ac magnetic field was successfully enhanced by the coverage with the shields, particularly the cross-shaped shield. It is inferred that the cross-shaped shield reduced flux trapping and jumping in the SQUID ring and at the edges of the pickup loops.