Thin-Film Superconducting Shields

To date, magnetic shields utilizing high-temperature superconductor materials mostly comprise bulk materials, usually shaped into a cylinder and then heat treated. We analyze the potential of thin-film technology, whereby a layer of superconductor is deposited on a substrate, to fabricate magnetic shields. Films deposited on a curved surface are inevitably granular, leading to reduced critical current density compared with crystalline films. This limits the maximum field that can be screened. Granular films also have an enhanced penetration depth compared with the bulk value, which determines the maximum possible screening at applied fields below the maximum. We demonstrate the utility of a mutual inductance measurement to evaluate small flat test samples of a granular film for their potential as a shielding material in a more complex geometry. This measurement predicts both the maximum magnetic field that can be screened and the residual leakage at fields below the maximum. The tested film was produced by the Electrophoretic deposition of YBCO on a silver substrate. The maximum screening field was comparable with that obtained for a similar film on a cylindrical substrate. We also show comparable results from a crystalline YBCO film.