Advances in magneto‐optical imaging applied to rock magnetism and paleomagnetism

Abstract

[1] We present results of the magneto-optical imaging technique applied to rock samples. This technique measures the magnetic flux threading a magneto-optically active film, which rotates the polarization direction of transmitted light (Faraday rotation) and is directly placed on the sample. Through the analyzer of a reflected light microscope, the vertical component of the surface magnetic field of the sample is observed and can be quantified through a specific calibration procedure. Owing to the thin magneto-optically active film (5 mm) and the small sample-to-film distance (∼1 mm), stray fields produced by magnetic grains in rocks carrying saturation isothermal remanent magnetization are successfully imaged with a spatial resolution of 10 mm. We can also image the surface field distribution of rocks carrying natural remanent magnetizations by modulating the analyzer angle. In addition to its high spatial resolution, this technique offers a direct comparison between magnetic and reflected light images. Therefore, this new technique appears to be a powerful tool to map and identify the carriers of magnetic remanence in rock samples.

Micrometer‐scale magnetic imaging of geological samples using a quantum diamond microscope

“…Standard paleomagnetic techniques, limited in part by the magnetometer sensitivity, typically measure the net magnetic moment of whole-rock samples with volumes of several cubic centimeters. For such samples, magnetic cleaning techniques such as thermal and alternating field demagnetization have been used to isolate the magnetization carried by sub-populations of ferromagnetic grains [Tauxe 2010]. However, magnetic cleaning often does not fully isolate a single population of grains due to overlapping ranges of unblocking temperatures or coercivities.…”

Magnetic, in situ, mineral characterization of Chelyabinsk meteorite thin section

“…SMM techniques have been considerably developed in the last few years (Uehara and Nakamura ; Uehara et al. ; Kletetschka et al. ).…”

“…The dominant technique for imaging magnetization distributions in geological samples is scanning magnetic microscopy (SMM) (Weiss et al 2007). SMM techniques have been considerably developed in the last few years (Uehara and Nakamura 2007;Uehara et al 2010;Kletetschka et al 2013). These scanners, however, have less sensitivity (our scanner has 10 À6 T, Uehara's 10 À5 T) than the superconducting scanner used at MIT that could sense magnetic anomalies in the 10 À9 T range (Weiss et al 2007).…”

Edge Contamination, Bulk Disorder, Flux Front Roughening, and Multiscaling in Type II Superconducting Thin Films

“…This method consists of placing a ferrimagnetic garnet indicator film (with a thickness of 5 µm) with in-plane anisotropy on top of the sample [44,45]. The component of the local magnetic induction B(r) perpendicular to the garnet film induces a Faraday rotation of the polarization of the light through the garnet.…”