Flux noise and flux creep in YBCO thin films
Abstract
We have used a dc SQUID to measure the low-frequency magnetic flux noise produced by thin-film rings of YBa2Cu3O sub 7-delta (YBCO) with various microstructures. Below the transition temperature T sub c of the YBCO, the spectral density of the noise scales as 1/f (f is the frequency) from 1 Hz to 1 kHz. This noise generally increases with temperature and vanishes abruptly at T sub c. Improvements in crystalline microstructure dramatically reduce the magnitude of the noise, which was lowest for a highly oriented sample with its c-axis perpendicular to the substrate. Making a radial cut to interrupt current paths around the sample ring does not significantly affect the magnitude of the noise, demonstrating that the noise arises from a local mechanism such as the thermally activated hopping of flux bundles. Flux creep was observed in one sample cooled in a magnetic field of 1 mT, and the creep rate exhibited a sharp maximum near 80 K. We conclude that SQUIDs and flux transformers of YBCO must be fabricated from highly oriented films to obtain low noise at low frequencies.
- Publication:
-
Presented at the Applied Superconductivity Conference
- Pub Date:
- August 1988
- Bibcode:
- 1988apsu.confQ....F
- Keywords:
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- Barium Compounds;
- Creep Properties;
- Magnetic Flux;
- Microstructure;
- Noise Reduction;
- Thin Films;
- Yttrium Compounds;
- Copper Oxides;
- Squid (Detectors);
- Superconducting Films;
- Temperature Dependence;
- Transition Temperature;
- Solid-State Physics