Abstract
The low-frequency noise in multiloop dc superconducting quantum interference device (SQUID) magnetometers fabricated from low-Tc (transition temperature) materials was investigated. The magnetometers are operated in a flux-locked loop based on additional positive feedback (APF). A simple noise reduction scheme for dc SQUIDs with APF is presented that eliminates the influence of critical current and resistance fluctuations without deteriorating the white noise performance. Applying this scheme to a magnetometer with a low-frequency two-level switching due to a single trap in the SixNy tunnel barrier reduced the switching amplitude of ≂10−3 Φ0 by at least two orders of magnitude down to a level below the intrinsic magnetometer flux noise. Using simple direct-coupled readout electronics with a 10 kHz bias reversal, a high bandwidth of ≂1 MHz, a low white flux noise of 1.5×10−6 Φ0/√Hz, and a 1/f noise corner frequency of 4 Hz have been measured.
Published Version
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