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Magnetic Shields for HTc SQUIDs
Kumiko IMAI Hironori MATSUBA Peter SPEAR Alistair FIFE
IEICE TRANSACTIONS on Electronics
Publication Date: 1993/08/25
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on High-Temperature Superconducting Electronics)
high Tc superconductor, magnetic shield, superconducting cylinder, Johnson noise,
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Bi2Sr2Ca1Cu2Ox thick film superconducting shields have been fabricated for use with HTc SQUIDs. Shielding factors and internal noise levels of the shields were measured using a DC SQUID magnetometer. A sample in which BSCCO was coated on the outside of a cylindrical Ag substrate exhibited larger noise levels than that with a sample in which BSCCO was coated on the inside of the Ag cylinder. The difference is explained by the thermally driven (Johnson) noise from the Ag substrate. A sample with the Ag cylinder outside the superconductor and samples with MgO substrates inside the superconductor showed good performance with a shielding factors of 10-8 and internal noise levels which did not exceed the DC SQUID magnetometer resolution (5 fTrms/Hz) at 4.2 K. In addition, the flux relaxation noise of BSCCO superconducting shields was estimated from the relaxation behavior of BSCCO.