High resolution magnetic microscopy using a DC SQUID

Using a 4.2 K Nb-PbIn DC superconducting quantum interference device (SQUID) with a 60- mu m inner hole side length, the authors have constructed a novel 1-D magnetic flux microscope with an unprecedented combination of spatial and magnetic field resolutions. During imaging, the sample is moved past the SQUID at a separation of about 38 mu m, and the output from the SQUID is recorded as a function of the sample position. The system achieves a spatial resolution of about 66 mu m and a magnetic field resolution of about 5.2 pTHz/sup -1/2/ at a frequency of 6 kHz. The microscope has been used to obtain susceptibility images of patterned superconducting samples in low fields, and a simple method for measuring static magnetic fields has been devised.>