High-Tc electronic planar gradiometer constructed from magnetometers on a chip

We have fabricated a high-T_c electronic planar gradiometer composed of dc SQUIDs on a 10 mm × 10 mm SrTiO₃ bicrystal substrate. The SQUIDs were patterned in a single-layer YBa₂Cu₃O_7-δ thin film which is prepared by pulsed laser deposition. The outputs of the magnetometers are added and subtracted by analog electronic circuits to form the gradiometer. These magnetometers could be used to construct two sets electronic planar first-order gradiometers or an electronic planar second-order gradiometer, which could measure the elements ∂B_z/∂x and ∂B_z/∂y or ∂²B_z/∂x∂y, respectively. The noise spectra of each magnetometer and a first-order electronic planar gradiometer were measured.