Jenny R. Holzer

High-resolution room-temperature sample scanning superconducting quantum interference device microscope configurable for geological and biomagnetic applications

We have developed a scanning superconducting quantum interference device (SQUID) microscope system with interchangeable sensor configurations for imaging magnetic fields of room-temperature (RT) samples with submillimeter resolution. The low-critical-temperature (Tc) niobium-based monolithic SQUID sensors are mounted on the tip of a sapphire and thermally anchored to the helium reservoir. A 25μm sapphire window separates the vacuum space from the RT sample. A positioning mechanism allows us to adjust the sample-to-sensor spacing from the top of the Dewar. We achieved a sensor-to-sample spacing of 100μm, which could be maintained for periods of up to four weeks. Different SQUID sensor designs are necessary to achieve the best combination of spatial resolution and field sensitivity for a given source configuration. For imaging thin sections of geological samples, we used a custom-designed monolithic low-Tc niobium bare SQUID sensor, with an effective diameter of 80μm, and achieved a field sensitivity of 1.5...

Monolithic low-transition-temperature superconducting magnetometers for high resolution imaging magnetic fields of room temperature samples

We have developed a monolithic low-temperature superconducting quantum interference device (SQUID) magnetometer and incorporated the device in a scanning microscope for imaging magnetic fields of room temperature samples. The instrument has a ∼100 μm spatial resolution and a 1.4 pT/Hz1/2 field sensitivity above a few hertz. We discuss design constraints on and potential applications of the SQUID microscope.

High-resolution imaging of cardiac biomagnetic fields using a low-transition-temperature superconducting quantum interference device microscope

We have developed a multiloop low-temperature superconducting quantum interference device sensor with a field sensitivity of 450 fT/Hz−1/2 for imaging biomagnetic fields generated by action currents in cardiac tissue. The sensor has a diameter of 250 μm and can be brought to within 100 μm of a room-temperature sample. Magnetic fields generated by planar excitation waves are associated with a current component parallel to the wave front, in agreement with predictions of the bidomain model. Our findings provide a new basis for interpreting the magnetocardiogram.

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.