Design and implementation of a scanning SQUID microscope

A cryogenic two-dimensional magnetic imaging system that incorporates a sensitive DC superconducting quantum interference device (SQUID) detector is described. In this instrument, which is called the scanning SQUID microscope, a flux transformer coupled to the SQUID is scanned over the surface of a planar sample by a room-temperature, stepping-motor-controlled manipulator with a positional resolution of about 2 mu m. With the present input coil, spatial resolution of 20 mu m and a flux sensitivity at the sample of 10/sup -5/ Phi /sub 0//Hz/sup 1/2/ is attainable. This system has been designed specifically to image the vortex structure and dynamics of weakly coupled superconductor arrays. >