Nanomagnetic properties of the meteorite cloudy zone

Abstract

Meteorites contain a record of their thermal and magnetic history, written in the intergrowths of iron-rich and nickel-rich phases that formed during slow cooling. Of intense interest from a magnetic perspective is the “cloudy zone,” a nanoscale intergrowth containing tetrataenite—a naturally occurring hard ferromagnetic mineral that has potential applications as a sustainable alternative to rare-earth permanent magnets. Here we use a combination of high-resolution electron diffraction, electron tomography, atom probe tomography (APT), and micromagnetic simulations to reveal the 3D architecture of the cloudy zone with subnanometer spatial resolution and model the mechanism of remanence acquisition during slow cooling on the meteorite parent body. Isolated islands of tetrataenite are embedded in a matrix of an ordered superstructure. The islands are arranged in clusters of three crystallographic variants, which control how magnetic information is encoded into the nanostructure. The cloudy zone acquires paleomagnetic remanence via a sequence of magnetic domain state transformations (vortex to two domain to single domain), driven by Fe–Ni ordering at 320 °C. Rather than remanence being recorded at different times at different positions throughout the cloudy zone, each subregion of the cloudy zone records a coherent snapshot of the magnetic field that was present at 320 °C. Only the coarse and intermediate regions of the cloudy zone are found to be suitable for paleomagnetic applications. The fine regions, on the other hand, have properties similar to those of rare-earth permanent magnets, providing potential routes to synthetic tetrataenite-based magnetic materials.

Variations in the Magnetic Properties of Meteoritic Cloudy Zone

“…In Esquel and Tazewell the entire kamacite signal in the cloudy zone is considered to be an artifact; it is solely composed of antitaenite and tetrataenite. This is supported by a scanning precession electron diffraction study of Tazewell in which no kamacite was observed in the cloudy zone (Einsle et al, 2018). In Estherville on the other hand, the width of the cloudy zone is significantly larger than the beam size.…”

“…The cloudy zone has been shown to be an excellent paleomagnetic recorder (Bryson et al, ; Einsle et al, ; Uehara et al, ). As the islands cool below 320 °C they transform to ordered tetrataenite.…”

“…For the most rapidly cooled IVA meteorites, the time available for Fe-Ni ordering is insufficient to allow tetrataenite formation, again leading to behavior that is unsuitable for paleomagnetic analysis. The most reliable paleomagnetic remanence is recorded by meteorites with intermediate cooling rates (∼ 2-500 • C Myr −1 ) which produces islands that are "just right" in both size and degree of Fe-Ni order.The cloudy zone has been shown to be an excellent paleomagnetic recorder Einsle et al, 2018;Uehara et al, 2011). As the islands cool below 320 • C they transform to ordered tetrataenite.…”

Atom Probe Tomography: Development and Application to the Geosciences

“…32.5% Ni isosurface is displayed in blue and Fe atoms in red (Einsle et al . ); (d) Pt and Fe atoms in isoferroplatinum. The inset is a 5 nm thick and 50 nm tall slice (figure 3 of Parman et al .…”

“…, Hellmann et al 2015, Gin et al 2017, diamond(Heck et al 2014, Lewis et al 2015, Schirhagl et al 2015, Mukherjee et al 2016, Fe-Ni metal alloys(Einsle et al 2018) and silicides(Gopon et al 2017), platinum-group alloys(Parman et al 2015, Daly et al 2017, oxides(Bachhav et al 2011, Fahey et al 2016, Taylor et al 2018, Frierdich et al 2019, Gamal El Dien et al 2019, Genareau et al 2019, Taylor et al 2019, carbonates(Felmy et al 2015, Branson et al 2016, P erez- Huerta et al 2016, P erez-Huerta and Laiginhas 2018, sulfides, Dubosq et al 2019, Gopon et al 2019, Wu et al 2019, sulfates(Weber et al 2016), zeolites(Schmidt et al 2019) and rock-forming silicates, such as feldspars(White et al 2018c, Cao et al 2019) and olivine(Bloch et al 2019, Cukjati et al 2019 …”