Thin sections were prepared and specific minerals were cut out under a binocular microscope using a non-magnetic diamond blade.
At 1930s, microscopes using electrons such as scanning electron microscope (SEM) [2] and transmission electron microscope (TEM) [3] were invented.
Using our MI magnetic microscope, a stray magnetic field distribution of the billow-like folds in the fault gouge in an isothermally magnetized state shows that the cohesive blackish gouges and the billow-like wavy folds are strongly magnetized, while the weathered granites are weakly or null magnetized (Fig. 2b; Additional file 1: Fig. S2).
Using a scanning magneto-impedance magnetic microscope and a scanning superconducting quantum interference device microscope, we observed surface stray magnetic field distributions over the folds, indicating that the folds and slip zones are strongly magnetized.
To determine the spatial distribution of ferrimagnetic minerals in Nojima fault gouge, we used a custom-made scanning MI magnetic microscope developed by Uehara and Nakamura (2007, 2008).
The same X Y Z coordinate system is used in Figs. 1d, e, 2a, b, 6, and Additional file 1: S2. d Macroscopic photograph of the fault gouge sample used for scanning magneto-impedance (MI) magnetic microscope observation.
However, our MI magnetic microscope is not able to detect weakly magnetized fault gouge.
The problem arises because modern microscopes use immersion lenses in which the sample sits in a high magnetic field.
The microscopes used in scanning microscopes are the atomic force microscope, laser force microscope, magnetic force microscope, electrostatic force microscope, scanning thermal microscope, scanning ion conductance microscope, and near-field scanning optical microscope.
Different techniques use different magnetic sensors, including the SQUID microscope (e.g., Fong et al. 2005; Weiss et al. 2007a, b), the magnetic tunnel junction microscope (e.g., Lima et al. 2014), and the magnetic microscope with nitrogen vacancy (NV) quantum diamond (Fu et al. 2014).
