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Magnetic characterization of non-ideal single-domain monoclinic pyrrhotite and its demagnetization under hydrostatic pressure up to 2 GPa with implications for impact demagnetization

Abstract : Here we present a comprehensive magnetic characterization of synthesized non-ideal single-domain (SD) monoclinic pyrrhotite (Fe 7 S 8). The samples were in the form of a powder and a powder dispersed in epoxy. ''Non-ideal " refers to a powder fraction of predominantly SD size with a minor contribution of small pseudo-single-domain grains; such non-ideal SD pyrrhotite was found to be a remanence carrier in several types of meteorites (carbonaceous chondrites, SNC.. .), which justifies the usage of synthetic compositions as analogous to natural samples. Data were collected from 5 to 633 K and include low-field magnetic susceptibility (χ0), thermomagnetic curves, major hysteresis loops, back-field remanence demagnetization curves, first-order reversal curves (FORCs), alternating field and pressure demagnetization of saturation isothermal remanent magnetization (SIRM), low temperature data (such as zero-field-cooled and field-cooled remanence datasets together with room temperature SIRM cooling–warming cycles) as well as XRD and Mössbauer spectra. The characteristic Besnus transition is observed at $33 K. FORC diagrams indicate interacting SD grains. The application of hydrostatic pressure up to 2 GPa using nonmagnetic high-pressure cells resulted in the demagnetization of the sample by 32–38%. Repeated cycling from 1.8 GPa to atmospheric pressure and back resulted in a total remanence decrease of 44% (after 3 cycles). Pressure demagnetization experiments have important implications for meteorite paleomagnetism and suggest that some published paleointensities of meteorites with non-ideal SD monoclinic pyrrhotite as remanence carrier may be lower limits because shock demagnetization was not accounted for.
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https://hal-amu.archives-ouvertes.fr/hal-01460781
Contributor : Pierre Rochette <>
Submitted on : Friday, February 24, 2017 - 9:52:56 AM
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Natalia S. Bezaevaa, Dmitriy A. Chareevd, Pierre Rochettee, Myriam Karsf, Jérôme Gattaccecae, et al.. Magnetic characterization of non-ideal single-domain monoclinic pyrrhotite and its demagnetization under hydrostatic pressure up to 2 GPa with implications for impact demagnetization. Meteoritics and Planetary Science, Wiley, 2016, ⟨10.1016/j.pepi.2016.05.009⟩. ⟨hal-01460781⟩

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