Magnetic microscopy using SQUIDs

SQUID-based magnetic microscopy involves scanning a sample closely past a low-noise SQUID. With the SQUID held in a flux-locked loop, a computer records the feedback output as a function of sample position and converts the resulting data into a false color image of magnetic field strength. Present systems have achieved spatial resolution down to about 5 mu m and flux resolution down to about 1 mu Phi(o)/Hz(1/2). They have been used to study the pairing symmetry of the high-T-c superconductors, for high-frequency imaging, and for a variety of applications related studies. Recently, microscopes have also been developed for high resolution magnetic imaging of room-temperature samples. We briefly describe the design, operation, and capabilities of these systems.