Resolving the Internal Magnetic Domain Structure of Cloudy Zone Tetrataenite

Abstract

Abstract Recent advances in magnetic imaging can directly capture the internal magnetization of natural and synthetic materials at resolutions <10 nm. This capability opens new possibilities to determine the magnetic domain state of ferromagnetic minerals that are fundamental for recording and retaining paleomagnetic records. Here, we present the highest resolution magnetic contrast images to date of tetrataenite islands in the cloudy zone of the Esquel pallasite meteorite obtained using circular dichroic soft X‐ray ptychography. These images, which have 4.4 nm spatial resolution, provide new insights into the magnetic structure of the cloudy zone, namely the prevalence of multidomain states, magnetostatic interactions, and islands with multiple “easy” magnetic axes. Our results demonstrate that the non‐interacting, single‐domain models used to derive cloudy‐zone paleointensities in previous studies require re‐evaluation. We additionally highlight the potential of high‐resolution ptychography to enhance our understanding of paleomagnetic remanence carriers in future work. Plain Language Summary Magnetic imaging provides a method of seeing the internal magnetic structures of both natural and synthetic materials. New advances now allow us to take these images with a resolution below 10 nm. We apply one of these techniques, called X‐ray ptychography, to image the magnetic structure of 150 nm “islands” of the mineral tetrataenite in an iron‐bearing meteorite at 4.4 nm resolution. To determine the presence of an ancient magnetic field and its strength, previous studies of this mineral assumed that the islands occupied a uniform magnetization state and were non‐interacting. However, these assumptions could not be tested as the previous studies used a magnetic imaging method that could not resolve the internal domain structure of the islands. Our magnetic imaging achieves this, and we find that most of the islands are not uniformly magnetized and interact with each other. Thus, existing ancient field intensity estimates should be reconsidered, and further work is needed to create models that accurately express how tetrataenite records magnetic fields. Additionally, we discuss the ways the geoscience community, particularly rock magnetists, could use ptychography to enhance our understanding of how minerals acquire and express their magnetic records. Key Points We image the magnetic domain structures of cloudy zone tetrataenite at 4.4 nm resolution using soft X‐ray dichroic ptychography The cloudy zone is comprised mostly of interacting, two‐domain and higher‐domain islands with single‐domain structures in the minority The sub‐10 nm resolution of X‐ray dichroic ptychography opens numerous avenues of research into magnetic domain state behavior