Planar SQUID gradiometers fabricated on 24/spl deg/ and 30/spl deg/ SrTiO/sub 3/ bicrystals

HTS dc SQUID gradiometers have been fabricated on 24/spl deg/ and 30/spl deg/ SrTiO/sub 3/ bicrystal substrates with slots and flux dams in the SQUID washers. The spatial response of such devices has been measured experimentally and compared with modelled results. Single layer devices, in terms of gradient sensitivity, have characteristics that deviate only slightly from idealized first order gradiometers. The low frequency flux noise of these devices is discussed with particular emphasis on both the unshielded properties and the effect of various cooldown procedures on the noise.