The magnetic structure and palaeomagnetic recording fidelity of sub-micron greigite (Fe3S4)

Valdez-Grijalva, Miguel A.; Nagy, Lesleis; Muxworthy, Adrian R.; Williams, Wyn; Fabian, Karl

doi:10.1016/j.epsl.2017.12.015

Cited by 17 publications

(27 citation statements)

References 31 publications

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“…Remanence characteristics of magnetic crystals are significantly affected by the grain morphology, and so we examine both cubic and spherical grain shapes of iron. The evolution of domain structure with grain size determined from unconstrained 3D micromagnetic models follows the well-established evolution seen in other materials (21,29,30) whereby the smallest particles have relaxation times of order 10 2 s or less and are termed superparamagnetic (SP). As particle size increases, grains become stable SD, followed by a transition to an unstable SV state and then to a stable SV state.…”

Section: Resultsmentioning

confidence: 64%

“…Thermal and Temporal Stability. Using similar NEB calculations to those we have previously applied (18,24,30), we determined energy barriers between various LEM states and calculated Pullaiah curves with relaxation times for both cubic and spherical iron grains. Fig.…”

Section: Resultsmentioning

confidence: 99%

“…12 and 38. Only recently has it been possible to attempt a comprehensive estimate of their thermal stability (18,24,30). As a consequence, the interpretation of paleomagnetic signals has hitherto been done on the basis of SD theory even though it has long been acknowledged that SD particles are unlikely to be the dominant remanence carriers (22).…”

Section: Discussionmentioning

confidence: 99%

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Thermomagnetic recording fidelity of nanometer-sized iron and implications for planetary magnetism

Nagy

Williams

Tauxe

et al. 2019

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

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Paleomagnetic observations provide valuable evidence of the strength of magnetic fields present during evolution of the Solar System. Such information provides important constraints on physical processes responsible for rapid accretion of the protoplanetesimal disk. For this purpose, magnetic recordings must be stable and resist magnetic overprints from thermal events and viscous acquisition over many billions of years. A lack of comprehensive understanding of magnetic domain structures carrying remanence has, until now, prevented accurate estimates of the uncertainty of recording fidelity in almost all paleomagnetic samples. Recent computational advances allow detailed analysis of magnetic domain structures in iron particles as a function of grain morphology, size, and temperature. Our results show that uniformly magnetized equidimensional iron particles do not provide stable recordings, but instead larger grains containing single-vortex domain structures have very large remanences and high thermal stability—both increasing rapidly with grain size. We derive curves relating magnetic thermal and temporal stability demonstrating that cubes (>35 nm) and spheres (>55 nm) are likely capable of preserving magnetic recordings from the formation of the Solar System. Additionally, we model paleomagnetic demagnetization curves for a variety of grain size distributions and find that unless a sample is dominated by grains at the superparamagnetic size boundary, the majority of remanence will block at high temperatures (∼100 °C of Curie point). We conclude that iron and kamacite (low Ni content FeNi) particles are almost ideal natural recorders, assuming that there is no chemical or magnetic alteration during sampling, storage, or laboratory measurement.

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Section: Resultsmentioning

confidence: 64%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Thermomagnetic recording fidelity of nanometer-sized iron and implications for planetary magnetism

Nagy

Williams

Tauxe

et al. 2019

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

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Section: Numerical Models Of MD Thermoremanencementioning

confidence: 99%

“…Once these energy barriers are found, they can be used to obtain relaxation times from the Arrhenius equation also used in Néel's SD and MD theories. This process has to be repeated for all temperatures in question and all grain sizes, geometries, and minerals of interest and has been done for magnetite cubes (Muxworthy et al, ) and more recently using the general micromagnetic model MERRILL (Conbhuí et al, ) for equidimensional magnetite cuboctahedra (Nagy et al, ), for greigite octahedra (Valdez‐Grijalva et al, ), and for iron cubes (Shah et al, ). While such micromagnetic models are on the rise and are undoubtedly physically most accurate, they have a number of shortcomings: (1) the great computing power necessary to calculate large particles limits them mostly to the PSD range, that is, vortex states rather than true MD states that contain DWs; (2) as the model has to be run for a particular grain geometry, a nearly infinite number of calculations would have to be done to cover all naturally occurring grain sizes and shapes; (3) unlike simple models like Néel's SD and MD theories, they do not allow an intuitive understanding of the underlying reasons for the remanence, as the results are obtained purely numerically; and (4) they require a level of detail of sample characterization to be run that is well beyond all but the most advanced paleomagnetic studies and hence are of limited use for most studies.…”

Section: Introductionmentioning

confidence: 99%

Theory of Stable Multidomain Thermoviscous Remanence Based on Repeated Domain Wall Jumps

Berndt

Chang

2018

JGR Solid Earth

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We developed a theory of multidomain (MD) thermoviscous remanence that can be solved analytically to yield an expression relating the blocking temperature of a MD grain to its relaxation time. This expression is analogous to Néel's widely used theory of single‐domain (SD) thermoviscous remanence but yields a different time‐temperature relationship. The theory is based on a two‐domain model with a domain wall (DW) that can jump between different pinning sites. In contrast to previous theories of this kind, our theory considers repeated DW jumps rather than a single jump in isolation. It is shown that while SD remanence behavior is fully described by the two quantities (V,HK0), that is, volume and microscopic coercivity, MD particle remanence depends on three quantities: volume, Barkhausen volume, and DW pinning field, denoted (V,VBark,HK0). “Pullaiah” nomograms of this new theory show that while small MD grains behave almost identically to SD grains, larger grains show different slopes depending on the above quantities. The theory predicts that MD grains can be highly stable remanence carriers, in particular showing a high thermal stability. Grains with weak pinning fields, however, while thermally stable, are highly unstable under alternating field (AF) demagnetization, being demagnetized under fields of a few millitesla. Our theory also explains (1) why samples dominated by MD grains show curved vector demagnetization plots for both thermal and AF demagnetization, as well as (2) why MD grains affect thermal demagnetization plots even at high temperatures, while their remanence is completely removed within the first few AF demagnetization steps.

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Size Ranges of Magnetic Domain States in Tetrataenite

Mansbach

Shah²,

Williams

et al. 2022

Preprint

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Paleomagnetic studies of meteorites provide unique constraints on the evolution of magnetic fields in the early solar system. These studies rely on the identification of magnetic minerals that can retain stable magnetizations over ≳4.5 billion years (Ga). The ferromagnetic mineral tetrataenite (γ''-Fe 0.5 Ni 0.5 ) is found in iron, stony-iron and chondrite meteorite groups. Nanoscale intergrowths of tetrataenite have been shown to carry records of paleomagnetic fields, although the effect of magnetostatic interactions on their magnetic remanence acquisition remains to be fully understood. Tetrataenite can also occur as isolated, non-interacting, nanoscale grains in many meteorite groups, although the paleomagnetic potential of these grains is particularly poorly understood. Here, we aim to improve our understanding of tetrataenite magnetization to refine our knowledge of existing paleomagnetic analyses and broaden the spectrum of meteorite groups that can be used for future paleomagnetic studies. We present the results of analytical calculations and micromagnetic modeling of isolated tetrataenite grains with various geometries. We find that tetrataenite forms a stable single domain state at grain lengths between 6 and ∼160 nm dependent on its elongation. It also possesses a magnetization resistant to viscous remagnetization over the lifetime of the solar system at 293 K. At larger grain sizes, tetrataenite's lowest energy state is a lamellar two-domain state, stable at Ga-scale timescales. Unlike many other magnetic minerals, tetrataenite does not form a single-vortex domain state due to its large uniaxial anisotropy. Our results show that single domain and two-domain tetrataenite grains carry an extremely stable magnetization and therefore are promising for paleomagnetic studies.Plain Language Summary Meteorites are fragments of small bodies created during the early solar system and therefore hold the key to understanding how planets formed and evolved. One way to further this understanding is by studying the magnetic fields recorded by these rocks. To do so requires the identification of magnetic minerals capable of retaining a record of an ancient field (in the form of a measurable magnetization) over the past 4.5 billion years. One mineral that is a potentially reliable recorder is tetrataenite (ordered Fe-Ni metal), which can be resistant to remagnetization by external fields greater than 1 T. The stability of a grain's magnetization is tied to its shape and size. Previous studies of magnetic minerals other than tetrataenite have found that the largest and smallest grains of most magnetic minerals are usually poor recorders with intermediate sizes being the most ideal. Here, we present the results of analytical calculations and numerical modeling of tetrataenite grains with various shapes and sizes to determine the conditions under which tetrataenite magnetization is stable over the lifetime of the solar system. We find that tetrataenite occupies a single-domain state (in which all magnetization is uniform t...

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The magnetic structure and palaeomagnetic recording fidelity of sub-micron greigite (Fe3S4)

Cited by 17 publications

References 31 publications

Thermomagnetic recording fidelity of nanometer-sized iron and implications for planetary magnetism

Thermomagnetic recording fidelity of nanometer-sized iron and implications for planetary magnetism

Theory of Stable Multidomain Thermoviscous Remanence Based on Repeated Domain Wall Jumps

Size Ranges of Magnetic Domain States in Tetrataenite

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