Scanning magnetic microscope system utilizing a magneto-impedance sensor for a nondestructive diagnostic tool of geological samples

We have developed a scanning magneto-impedance (MI) magnetic microscope to image surface stray magnetic fields of room-temperature geological samples with submillimeter resolution. The instrument consists of a small, 30 microm diameter, 5 mm length amorphous wire-based magneto- impedance (MI) sensor without any cooling mechanisms. The spacing between the sensor head and the sample was less than 300 microm. The length of the amorphous wire and sample-to-wire distance limits the spatial resolution. We have achieved a spatial resolution of 400 microm with a magnetic resolution of 10 nT. This instrument enables us to map a two-dimensional out-of-page component of a stray magnetic field of a natural remanent magnetization over a millimeter-thick slab of a primitive ordinary chondrite meteorite, documenting dipolelike features. A comparison of element mapping images with the stray field of the meteorites reveals what individual metals carry the dipolar remanences in the meteorites. These results suggest that the scanning MI microscope offers a room-temperature operable, small, low-maintenance alternative to the scanning SQUID microscope, and can aid in the interpretation of the magnetic remanence acquisition process of a meteorite.