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A dc-SQUID planar gradiometer has been fabricated with YBa2Cu3O7-δ step-edge Josephson junctions on a 10mm×10mm single crysta l SrTiO3 ［100］ substrate. The gradiometer has a pair of pickup loop s with an area of 33 mm2 and the baseline of 45mm. The system opera tes well in unshielded environment. A rejection of common mode fields of 14×1 02 in all directions and a field gradient sensitivity (white noise) b etter than 8pT/cmHz at 77K have been achieved.

In this paper, we report the time dependence of the magnetic field inside a YBa2Cu3O7 tube, when switching on a field He outside the tube after a zero field cooling the tube into a superconducting state. In our experiment He is smaller than 4Hrm, where Hrm is the trapped field of the tube. The dependence can be expressed as Hi(t)=H0 + B0(Int + 1-exp(-t/τ)), where H0, B0 and 1/τ are functions of He, and they keep rising when He>Hrm. We suggest that the term of Int is caused by flux lines creeping, while (1-exp(-t/τ)) results from flux lines fluctuating, which is a short time effect. The shielding effect of YBa2Cu3O7 tubes is perfect for low dc field (rm/2), and better than the best normal metal for ac magnetic noise.