We describe a direct-current superconducting quantum interference device (SQUID) first-order gradiometer fabricated from a single layer of YBa2Cu3O7
on a 30×10 mm2
bicrystal substrate. The device has a baseline of 13 mm and an intrinsic balance of ∼ 10−3.
The gradient sensitivity at 77 K and 1 kHz is 50 fT/(cm)
in magnetic shielding and 260 fT/(cm)
when operated unshielded in our laboratory. An antiparallel two-SQUID coupling scheme is employed to optimize the device’s balance to at least 3×10−5.
© 1999 American Institute of Physics.