No abstract

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/(cmHz) in magnetic shielding and 260 fT/(cmHz) 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.

HTS dc gradiometers have been fabricated with slots and flux dams in their SQUID washers. Using a single layer of YBCO, the gradient sensitivity is limited by the sensing magnetometer in the centre of the structure. The spatial response of such devices has been measured experimentally indicating that single layer devices, in terms of gradient sensitivity, have characteristics that deviate slightly from idealized first order gradiometers. The flux noise of these devices is discussed with particular emphasis on their unshielded low frequency noise properties. We also discuss the effect of different cooldown procedures on the flux noise.

First-order HTS SQUID gradiometers were fabricated on 30 × 10 mm2 bicrystal substrates. These devices have a baseline of 13 mm, intrinsic balance levels of ~1/700 and a typical gradient sensitivity at 1 kHz of 79 fT cm-1 Hz-1/2. A two-SQUID coupling scheme is discussed that further enhances the device's ability to reject uniform fields.

Thin films of YBazCu307., (YBCO) andNdBazCu307., (NBCO) were grown by pulsed laser deposition (PLD). The experiment was planned using experimental design to investigate the relative importance of the individual growth parameters for the properties of the films. For both materials critical temperatures close to 90K were obtained. The electrical and morphological properties of the films were correlated to the growth conditions using regression analysis. For NBCO, regions where both electrical and morphological properties were optimised could be found, while for YBCO we found that the main factors that lead to high critical temperatures also lead to a substantial increase in the surface roughness.