A high spatial resolution synchrotron Mössbauer study of the Tazewell <scp>IIICD</scp> and Esquel pallasite meteorites

Blukis, Roberts; Rüffer, R.; Chumakov, A. I.; Harrison, R. J.

doi:10.1111/maps.12841

Cited by 23 publications

(40 citation statements)

References 43 publications

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“…We therefore suggest that for cooling rates < 150 • C Myr −1 , there is sufficient time for ordering and cloudy zone islands are formed of tetrataenite, while at cooling rates exceeding 2500 • C Myr −1 the islands do not order and remain as taenite. We do not observe superparamagnetic behavior (in which case the cloudy zone would appear unmnagetized on our observation timescales) because this behavior is likely to be suppressed by interactions with neighboring particles (Varón et al, 2013) and surface effects (Blukis et al, 2017). The drastic change in magnetic properties associated with this ordering suggests that the fastest cooled meteorites are not able to record paleomagnetic information; this only occurs if tetrataenite forms (Einsle et al, 2018;Gattacceca et al, 2014).…”

Section: Variations In Cloudy Zone Behavior With Cooling Ratementioning

confidence: 81%

“…Cooling rates in the mesosiderites are so slow that the cloudy zone undergoes further breakdown; the islands develop Fe‐rich interiors and kamacite is observed in the matrix (Yang et al, ). We expect the magnetic properties of the cloudy zone to inherently change if the matrix becomes ferromagnetic kamacite, rather than paramagnetic antitaenite which is observed in faster cooled samples (Blukis et al, ; Einsle et al, ).…”

Section: Discussionmentioning

confidence: 99%

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Variations in the Magnetic Properties of Meteoritic Cloudy Zone

Nichols¹,

Bryson

Blukis

et al. 2020

Geochem Geophys Geosyst

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Iron and stony‐iron meteorites form the Widmanstätten pattern during slow cooling. This pattern is composed of several microstructures whose length‐scale, composition and magnetic properties are dependent upon cooling rate. Here we focus on the cloudy zone: a region containing nanoscale tetrataenite islands with exceptional paleomagnetic recording properties. We present a systematic review of how cloudy zone properties vary with cooling rate and proximity to the adjacent tetrataenite rim. X‐ray photoemission electron microscopy is used to compare compositional and magnetization maps of the cloudy zone in the mesosiderites (slow cooling rates), the IAB iron meteorites and the pallasites (intermediate cooling rates), and the IVA iron meteorites (fast cooling rates). The proportions of magnetic phases within the cloudy zone are also characterized using Mössbauer spectroscopy. We present the first observations of the magnetic state of the cloudy zone in the mesosiderites, showing that, for such slow cooling rates, tetrataenite islands grow larger than the multidomain threshold, creating large‐scale regions of uniform magnetization across the cloudy zone that render it unsuitable for paleomagnetic analysis. 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.

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Section: Variations In Cloudy Zone Behavior With Cooling Ratementioning

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Variations in the Magnetic Properties of Meteoritic Cloudy Zone

Nichols¹,

Bryson

Blukis

et al. 2020

Geochem Geophys Geosyst

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“…Finite-element micromagnetic simulations were performed initially using roomtemperature micromagnetic parameters appropriate to cubic disordered Fe0.5Ni0.5 (Ms = 1,273 kA/m, K1 = 1 kJ/m 3 , Aex = 1.13 ×10 −11 J/m), which is a soft ferromagnet below its Curie temperature of ∼450 • C (18,19). The matrix phase is not included in the micromagnetic models, since Mössbauer spectroscopy demonstrates that the matrix phase is paramagnetic in the bulk cloudy zone (20,21). All three islands adopted either single-or double-vortex states at remanence ( Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Previous suggestions that this effect was due to exchange coupling between islands via the matrix are contingent on the matrix phase being ferromagnetic (6,7). High-resolution Mössbauer spectroscopy measurements have since shown that the matrix is paramagnetic in the bulk phase and only appears ferromagnetic at surfaces and in thin films (21). With a paramagnetic matrix, magnetostatic interactions between islands provide an alternative mechanism leading to strong alignment.…”

Section: The Origin Of Optimal Hard Magnetic Properties In the Fine Cmentioning

confidence: 99%

Nanomagnetic properties of the meteorite cloudy zone

Einsle

Eggeman

Martineau

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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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.

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“…Using X-ray photoemission electron microscopy (XPEEM), the magnetization of the CZ alone can be measured at the nm-scale along several kamacite/taenite interfaces and used to calculate the relative orientation and the intensity of the ambient magnetic field present when the CZ grew. Blukis et al (2017) posed four fundamental questions that should be addressed in order to obtain more accurate paleointensity estimates from XPEEM images of the CZ: 1) What is the magnetic state of islands when they form? 2) What is their blocking temperature and how is their remanence changed when cooling through this temperature?…”

Section: Introductionmentioning

confidence: 99%

Meteorite cloudy zone formation as a quantitative indicator of paleomagnetic field intensities and cooling rates on planetesimals

Maurel

Weiss

Bryson

2019

Earth and Planetary Science Letters

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Metallic microstructures in slowly-cooled iron-rich meteorites reflect the thermal and magnetic histories of their parent planetesimals. Of particular interest is the cloudy zone, a nanoscale intergrowth of Ni-rich islands within a Ni-poor matrix that forms below ~350°C by spinodal decomposition. The sizes of the islands have long been recognized as reflecting the lowtemperature cooling rates of meteorite parent bodies. However, a model capable of providing quantitative cooling rate estimates from island sizes has been lacking. Moreover, these islands are also capable of preserving a record of the ambient magnetic field as they grew, but some of the key physical parameters required for recovering reliable paleointensity estimates from magnetic measurements of these islands have been poorly constrained. To address both of these issues, we present a numerical model of the structural and compositional evolution of the cloudy zone as a function of cooling rate and local composition. Our model produces island sizes that are consistent with present-day measured sizes. This model enables a substantial improvement in the calibration of paleointensity estimates and associated uncertainties. In particular, we can now accurately quantify the statistical uncertainty associated with the finite number of islands acquiring the magnetization and the uncertainty on their size at the time of the record. We use this new understanding to revisit paleointensities from previous pioneering paleomagnetic studies of cloudy zones. We show that these could have been overestimated by up to one order of magnitude but nevertheless still require substantial magnetic fields to have been present on their parent bodies.Our model also allows us to estimate absolute cooling rates for meteorites that cooled slower than < 10,000°C My -1 . We demonstrate how these cooling rate estimates can uniquely constrain the low-temperature thermal history of meteorite parent bodies. Using the main-group pallasites as an example, we show that our results are consistent with the previously-proposed unperturbed, conductive cooling at low temperature of a ~200-km radius main-group pallasite parent body.

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A high spatial resolution synchrotron Mössbauer study of the Tazewell IIICD and Esquel pallasite meteorites

Cited by 23 publications

References 43 publications

Variations in the Magnetic Properties of Meteoritic Cloudy Zone

Variations in the Magnetic Properties of Meteoritic Cloudy Zone

Nanomagnetic properties of the meteorite cloudy zone

Meteorite cloudy zone formation as a quantitative indicator of paleomagnetic field intensities and cooling rates on planetesimals

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