We have designed and operated a magnetic flux microscope which measures the magnetic field above a sample surface by scanning a 4.2 K thin-film dc superconducting quantum interference device (SQUID) along one direction. With the SQUID and sample separated by about 160 μm, the system can image features with a spatial resolution of about 220 μm and a magnetic field resolution of 1.8×10−13 THz−1/2. We have used the system to view trapped magnetic flux, to image thin-film strips of superconducting Pb in field strengths of 0–750 nT, and to monitor the position of a sample with a resolution of approximately 0.5 nm Hz−1/2 at a frequency of 4 kHz.
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Mathai et al. (1992) studied this question.
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