We have developed scanning probe magnetic microscopes which use dc Superconducting QUantum Interference Devices (SQUIDs) to obtain images of the magnetic field above a sample surface. In our instruments, the SQUID is held fixed and the sample is scanned in a raster pattern by means of a computer-controlled cryogenic positioning mechanism. We record the output of the SQUID as a function of sample position and use this to construct gray-scale or false color images of the magnetic field above the sample. We presently have two microscopes which can scan in 3D; one microscope uses a high transition temperature ((Tau) _c) YBa₂Cu₃O₇ SQUID while the other microscope uses a low-(Tau) _c Nb-PbIn SQUID. Our high-(Tau) _c microscope operates with the sample and SQUID in liquid nitrogen and typically achieves a spatial resolution of about 20-80 micrometers and a magnetic field resolution of about 20-200 pT for a 1 second average. Our low-(Tau) _c microsope operates with the sample and SQUID in a liquid-helium cooled vacuum space and is designed to allow the imaging of samples at different temperatures. We report on the microscopic magnetic imaging of currents, ferromagnetic inks, superconducting films and normal metal samples.

Date Published: 2 July 1994
PDF: 12 pages
Proc. SPIE 2160, Superconductive Devices and Circuits, (2 July 1994); doi: 10.1117/12.180995

Published in SPIE Proceedings Vol. 2160:
Superconductive Devices and Circuits
Robert A. Buhrman; John T. Clarke; Ken Daly; Roger H. Koch; Jerome A. Luine; Randy W. Simon, Editor(s)