High-transition temperature superconducting quantum interference device microscope

A microscope has been constructed in which a high-transition temperature dc superconducting quantum interference device (SQUID) in vacuum is brought to within 140 mu m of samples at room temperature and pressure. The SQUID is mounted on the upper end of a sapphire rod, cooled to liquid nitrogen temperature, below a 75-mu m thick sapphire window. Samples can either be placed directly on the window or scanned over the SQUID to produce magnetic images. A square-washer SQUID with inner and outer dimensions of 30 and 50 mu m can resolve 130 mu m magnetic features. The instrument is intended primarily for biological applications. (C) 1996 American Institute of Physics.