Low-Frequency Noise of High Tc Superconducting Quantum Interference Device (SQUID) Magnetometer Fabricated on Bicrystal Substrate

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Abstract
The excess low-frequency noise of a high T c superconducting quantum interference device (SQUID) magnetometer fabricated on bicrystal substrate is studied. Direct-coupled magnetometers are fabricated using different geometries of the pickup coil, and the relationship between the geometry of the pickup coil and the low-frequency noise of the magnetometer is studied. It is shown that the weak superconducting region in the pickup coil, which is automatically formed on top of the grain boundary of the bicrystal substrate, is one of the main sources of the excess noise. By selecting an appropriate geometry of the pickup coil, we can significantly decrease the excess noise of the magnetometer without decreasing its effective area.