High-Resolution directly coupled monolithic SQUID Magnetometer for imaging Magnetic Fields
Abstract
We have designed and fabricated a monolithic, directly coupled niobium superconducting quantum interference device (SQUID) magnetometer and incorporated the device in a scanning microscope for imaging magnetic fields of room-temperature (RT) samples with sub-millimeter resolution. The SQUID chip is mounted on the tip of a sapphire rod in the vacuum space of the cryostat; typically separated from the RT sample by < 75 μm, including a thin sapphire window. The sapphire rod is anchored to the helium reservoir and shielded from radiation by a nitrogen-cooled cone. A computerized non-magnetic scanning stage with sub-micron resolution allows a RT sample to be scanned below the sapphire window. For a 125 μm diameter pickup coil directly coupled to a washer SQUID with a 10 μm hole, we achieved a flux noise of 7 μ φ_o/Hz^1/2 resulting in a field sensitivity of 6 pT/Hz^1/2 for frequencies above 1 Hz. This results in a moment sensitivity of 5.4 × 10-18 Am^2/Hz^1/2 and a minimum detectable current of 1 nA/Hz^1/2 at a sample to sensor distance of 75 μm. The SQUID microscope was used to image the distribution of time-dependent stimulus or action currents in anisotropic cardiac tissue, the remnant magnetization of the Martian meteorite ALH84001 and lunar samples, the detection of magnetic nanoparticles and biogenic magnetite.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2002
- Bibcode:
- 2002APS..MARS13002F