Ultra-high Sensitivity Moment Magnetometry of Geological Samples Using Magnetic Microscopy

TL;DR

This paper introduces a novel technique for accurately determining the magnetic moments of geological samples using magnetic microscopy, enabling detection of extremely weak magnetization with high spatial resolution and improved contamination identification.

Contribution

The authors developed a unique method to extract net magnetic moments from magnetic microscopy data, validated it with synthetic and real samples, and demonstrated its superiority over standard magnetometers.

Findings

Successfully measured moments down to 10^-15 Am2

Net moments closely match standard magnetometer results

Enhanced ability to identify magnetic contamination

Abstract

Paleomagnetically useful information is expected to be recorded by samples with moments up to three orders of magnitude below the detection limit of standard superconducting rock magnetometers. Such samples are now detectable using recently developed magnetic microscopes, which map the magnetic fields above room-temperature samples with unprecedented spatial resolutions and field sensitivities. However, realizing this potential requires the development of techniques for retrieving sample moments from magnetic microscopy data. With this goal, we developed a technique for uniquely obtaining the net magnetic moment of geological samples from magnetic microscopy maps of unresolved or nearly unresolved magnetization. This technique is particularly powerful for analyzing small, weakly magnetized samples such as meteoritic chondrules and terrestrial silicate crystals like zircons. We validated this technique by applying it to field maps generated from synthetic sources and also to field maps measured using a superconducting quantum interference device (SQUID) microscope above geological samples with moments down to 10^-15 Am2. For the most magnetic rock samples, the net moments estimated from the SQUID microscope data are within error of independent moment measurements acquired using lower sensitivity standard rock magnetometers. In addition to its superior moment sensitivity, SQUID microscope net moment magnetometry also enables the identification and isolation of magnetic contamination and background sources, which is critical for improving accuracy in paleomagnetic studies of weakly magnetic rocks.