LTS SQUID /spl radic/???? Microscopy: A Leap in sensitivity?.

Room-temperature (RT) sample scanning superconducting quantum interference device (SQUID) microscopy (SSM) is a very powerful and promising technique for imaging magnetic field distributions . A SQUID microscope with interchangeable sensor configurations for imaging magnetic fields of room-temperature (RT) samples with sub-millimeter resolution was developed. The sensors are mounted in the vacuum space of a cryostat and thermally anchored to the helium reservoir. A positioning mechanism allows us to adjust the sample-to-sensor spacing from the top of the Dewar. Combining microfluidic based devices and SQUID microscopy allows us to identify a moving single micron sized ferromagnetic particles with a magnetic moment of 10^-14 Am² at a bandwidth of 2.5 KHz and a sensor to particle spacing of 95 mum. Although magnetic force microscopes (MFMs) have better moment sensitivities than SQUID microscopes, the current generation of SQUID microscopes have field sensitivities 105 times better than the MFM and do not suffer from the sample-instrument interactions that plague MFM-sensing of magnetically soft materials.