Magnetic Shields for HTc SQUIDs

Kumiko IMAI  Hironori MATSUBA  Peter SPEAR  Alistair FIFE  

IEICE TRANSACTIONS on Electronics   Vol.E76-C   No.8   pp.1280-1286
Publication Date: 1993/08/25
Online ISSN: 
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.