[S-EM15] Geomagnetism, paleomagnetism and rock magnetism

[SEM15-07] In-situ Localization of Dipoles in Thin Sections by Merging Scanning SQUID Magnetic Microscopy with Optical Imaging

★Invited Papers

*Joseph Kirschvink¹, Atsuko Kobayashi¹, Hironori Hidaka², Kotaro Kawai³ (1.Earth-Life Science Institute, Tokyo Institute of Technology, 2.Department of System and Control Engineering, Tokyo Institute of Technology, 3.Department of Mechanical Engineering, Tokyo institute of Technology)

Keywords:Paleomagnetism, Biomagnetism, Rock Magnetism, Micromagnetic Analysis

Magnetic microscopy capable of localizing deposits of ferromagnetic minerals in biological and geological materials is an emerging technology in the natural sciences. Applications range from acquiring paleomagnetic and rock magnetic information from sub-mm scale features, to the localization of natural deposits of ferromagnetic minerals like magnetite in biological tissues, including those of possible sensory organs in migratory animals. Of the several forms of magnetic images, including scanning fluxgates, scanning SQUID sensors, Quantum-Diamond technologies and Atomic Force Microscopy, the scanning SQUID technology offers resolution at a special scale and depth sensitivity suitable for analyzing many petrographical and histological grain sizes, and cellular-sized biological structures. A major problem in this entire field, however, is the accurate localization of the magnetic dipole features relative to the sample being scanned, such that follow-up studies could be conducted. It is also important to bring this technology into a format that makes analyses user-friendly, and facilitates more focused studies using HRTEM, FIB, synchrotron, and other nano-analytical methods.
We report here the development of new techniques for co-locating the magnetic and optical images of thin-sections being scanned. These include the use of ultra-high purity fused-quartz plates with a laser-engraved grid system, a minimally-magnetic camera / lens assembly that views geological or histological thin sections from below, software for positioning of the SQUID chip sensors relative to the grid, and enhanced calibration and clean-lab environments. This SQUID assemblies like used here will be easily implemented on the scanning squid microscopes that rely on cryogen-free pulse tube technology, but in principle could be retrofit to systems still that rely on liquid helium. We will show examples of biological and geological applications.