Mapping the Phase Space of Fe-Ni alloys in Meteorites: revealing the chemical and crystallographic complexity of REE-free magnet analogues

Rare-earth permanent magnets play a critical role in green technologies such as wind turbines and electric vehicles. These elements are mainly sourced from a limited number of countries, many of which suffer from complex political situations. A desire for secure and ethical materials drives a strong global interest

in developing low-cost alternatives for permanent magnetic materials. For over 20-years the meteoritic mineral tetrataenite has promised one such solution due to excellent magnetic properties arising from its crystallographic and chemical structure. Recent advances in synthesis have finally started to produce

large volumes of this mineral synthetically. However, this has brought to focus new questions about the role of minor and trace elements as well as cooling rate in the formation of this extra-terrestrial alloy. Particular focus for this project will be on the formation of the nanoscale intergrowth called the cloudy

zone. It possesses a high magnetic coercively due to the combination of small tetrataenite particles (<100 nm) being embedded in a different Fe-Ni alloy matrix. These properties provide a natural analogue to rare-earth permanent magnet materials. The project plans to re-map the Fe-Ni phase space represented in the wide range of cooling rates and

compositions contained in meteorite samples available. The chemical and crystallographic information will be combined with magnetic characterisation to develop structure-function relationships. I plan to employ a range of machine learning tools to design sampling strategies as well as leverage out 'hidden'

details in the often large and complex microanalysis data collected. Sample analysis will work across length scales to understand how the cloudy zone forms and to understand the role of trace and minor element diffusion in controlling its formation. This will include scanning and transmission electron

microscopy, energy dispersive spectroscopy, electron back scatter diffraction, as well as atom probe tomography. These multi-scale datasets will be combined to form digital twins of the samples which offer quantitative insight into the formation of the cloudy zone. Due to the length scale of the cloudy zone, as described in 'Discovery and Implications of hidden

Atomic-Scale Structure in a Metallic Meteorite' (2021), atom probe tomography has been identified as a characterisation technique with a fine resolution to study this effectively. As it has been shown in 'Nanomagnetic properties of the meteorite cloudy zone' (2018) that these samples can be successfully

studied with this technique, I believe continued analysis via this route is best suited for this project. I have significant experience with this characterisation technique and therefore believe that I would be a suitable candidate for this research. Furthermore, as APT samples can only observe a small amount of material at

any time, samples will also be studied with more typical characterisation techniques, such as TEM, SEM, EDS, and WDS, so that a holistic understanding of the composition and microstructure of the naturally occurring material to be obtained. This wider view will also allow for the influence of trace and minor

elements in the formation of this cloudy zone to be assessed, which may provide insight into alloying additions to improve the outcome of further cloudy zone synthesis experiments.