Increasing the Accuracy and Efficiency of Micromagnetic Tomography by Double Sided Scanning

Abstract

Paleomagnetic data are usually retrieved by subjecting bulk samples, e.g. lavas, to laboratory measurement protocols. In many instances, these protocols yield uninterpretable results caused by the presence of particles with adverse magnetic properties that blur the signal of the reliable magnetic particles. With Micromagnetic Tomography (MMT) we focus on identifying the signal of particles with reliable properties. Their individual magnetic moments are computed by scanning the surface of a ~3 mm2 thin section with a quantum diamond microscope (QDM) and locating the magnetic recorders with computed tomography. Currently, almost 80% of all resolved magnetic moments is discarded due to numerical instability, making it difficult to obtain statistically relevant paleointensities and paleodirections based on the remaining magnetic moments. We improve the number of reliable magnetic moments from MMT experiments by making a QDM scan of both sides of the sample. Here, we conduct a combined numerical and empirical study to investigate the benefits and difficulties of adding this double-sided scanning (DSS) protocol to MMT. By investigating the theoretical gain of DSS for varying sample thicknesses, we show that DSS returns three times more numerically stable magnetic moments compared to single sided scanning for a sample thickness of 50 μm. However, careful sample preparation and handling is required: best results are obtained when both sample surfaces are measured as parallel as possible, while keeping the sample intact when flipping it to the other side for the bottom measurement. By overcoming these difficulties, DSS will provide a significant boost in stable magnetic moments.