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Magnetic Characterization of Non-Ideal Single-Domain Monoclinic Magnetic characterization of non-ideal single-domain monoclinic pyrrhotite and its demagnetization under hydrostatic pressure up to 2 GPa with implications for impact demagnetization Natalia S. Bezaevaa, Dmitriy A. Chareevd, Pierre Rochettee, Myriam Karsf, Jérôme Gattaccecae, Joshua M. Feinbergg, Ravil A. Sadykovh, Dilyara M. Kuzinac, Sergey N. Axenovh To cite this version: 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 demagnetiza- tion 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 HAL Id: hal-01460781 https://hal-amu.archives-ouvertes.fr/hal-01460781 Submitted on 24 Feb 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Physics of the Earth and Planetary Interiors 257 (2016) 79–90 Contents lists available at ScienceDirect Physics of the Earth and Planetary Interiors journal homepage: www.elsevier.com/locate/pepi Magnetic characterization of non-ideal single-domain monoclinic pyrrhotite and its demagnetization under hydrostatic pressure up to 2 GPa with implications for impact demagnetization ⇑ Natalia S. Bezaeva a,b,c, , Dmitriy A. Chareev d,b, Pierre Rochette e, Myriam Kars f, Jérôme Gattacceca e, Joshua M. Feinberg g, Ravil A. Sadykov h, Dilyara M. Kuzina c, Sergey N. Axenov h a Faculty of Physics, M.V. Lomonosov Moscow State University, Leninskie Gory, 119991 Moscow, Russia b Ural Federal University, 19 Mira Str., 620002 Ekaterinburg, Russia c Kazan Federal University, 18 Kremlyovskaya Str., 420000 Kazan, Russia d Institute of Experimental Mineralogy, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia e Aix-Marseille Université, CNRS, IRD, CEREGE UM34, Technopôle de l’Environnement Arbois-Mediterranée, BP80, 13545 Aix-en-Provence, France f Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku 783-8502, Japan g Institute for Rock Magnetism, Dept. of Earth Sciences, University of Minnesota, Minneapolis, MN 55455, United States h Institute for Nuclear Research, Russian Academy of Sciences, Prospekt 60-letiya Oktiabria 7a, 117312 Moscow, Russia article info abstract Article history: Here we present a comprehensive magnetic characterization of synthesized non-ideal single-domain Received 9 September 2015 (SD) monoclinic pyrrhotite (Fe7S8). The samples were in the form of a powder and a powder dispersed Received in revised form 31 March 2016 in epoxy. ‘‘Non-ideal” refers to a powder fraction of predominantly SD size with a minor contribution Accepted 12 May 2016 of small pseudo-single-domain grains; such non-ideal SD pyrrhotite was found to be a remanence Available online 21 May 2016 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 Keywords: include low-field magnetic susceptibility (v ), thermomagnetic curves, major hysteresis loops, back- Non-ideal single-domain monoclinic 0 field remanence demagnetization curves, first-order reversal curves (FORCs), alternating field and pres- pyrrhotite Magnetic properties sure demagnetization of saturation isothermal remanent magnetization (SIRM), low temperature data Pressure demagnetization (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 pres- sure 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 mete- orites with non-ideal SD monoclinic pyrrhotite as remanence carrier may be lower limits because shock demagnetization was not accounted for. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction of paleomagnetic and rock magnetic significance due to its wide occurrence in a considerable variety of natural environments, ter- It is now recognized that the ferrimagnetic iron sulfide Fe7S8 restrial rocks and meteorites (Arnold, 1967; Sassen et al., 1989; known as monoclinic pyrrhotite (4C superstructure) is a mineral Rochette et al., 1990, 2005; Cournede et al., 2015; Tikoo et al., 2015). Single-domain (SD) pyrrhotite is also a candidate magnetic mineral for the Martian magnetic anomalies (Dunlop and Arkani- ⇑ Corresponding author at: Faculty of Physics, M.V. Lomonosov Moscow State Hamed, 2005; Rochette et al., 2005). Additionally, Gilder et al. University, Leninskie Gory, 119991 Moscow, Russia. (2011) discuss pyrrhotite inclusions hosted by diamonds and argue E-mail addresses: [email protected] (N.S. Bezaeva), [email protected] (D.A. Chareev), [email protected] (P. Rochette), [email protected] (M. Kars), that these inclusions act as geobarometers, preserving information [email protected] (J. Gattacceca), [email protected] (J.M. Feinberg), rsadykov@ about the pressure conditions under which the diamonds formed inr.ru (R.A. Sadykov), [email protected] (D.M. Kuzina), [email protected] in the Earth’s mantle. (S.N. Axenov). http://dx.doi.org/10.1016/j.pepi.2016.05.009 0031-9201/Ó 2016 Elsevier B.V. All rights reserved. 80 N.S. Bezaeva et al. / Physics of the Earth and Planetary Interiors 257 (2016) 79–90 The magnetic properties of both natural and synthetic pyrrho- perature synthesis is necessary to avoid the production of hexago- tites, including their grain-size dependence, have been the subject nal rather than monoclinic pyrrhotite. This particular synthesis of several rock magnetic studies (e.g., Clark (1984), Dekkers (1988), method also differs from the hydrothermal method in the compo- Rochette et al. (1990), Menyeh and O’Reilly (1997)). Monoclinic sition of liquid medium as well as by the use of quartz ampoules pyrrhotite is characterized by three characteristic transitions. First instead of autoclaves. In this study monoclinic pyrrhotite was pro- is the temperature-induced ferrimagnetic-to-paramagnetic phase duced in evacuated quartz ampoules using the low-melting eutec- transition, which occurs upon reaching the Curie temperature tic KCl/AlCl3 flux with melting point lower than 427 K (Moh and (593–598 K). Second is the low-temperature magnetic transition Taylor, 1971). The starting materials were iron powder Merck or so-called Besnus transition at 30–34 K (Besnus and Meyer, (99.5%, 10 lm), crystalline sulfur Johnson Matthey (99.9995%), 1964; Rochette et al., 2011). This transition has a crystallographic KCl and anhydrous AlCl3 (Fluka, 98%). Quartz ampoules were rather than magnetic origin (Wolfers et al., 2011) and is often used heated up to 523–528 K in vertical nongradient tube furnaces over as a diagnostic indicator of the presence of pyrrhotite. Third is the 1–2 h, and then held at this synthesis temperature for three pressure-induced ferrimagnetic-to-paramagnetic transition, which months. Appropriate synthesis temperatures and Fe/S ratios were occurs at 2.8 GPa according to Rochette et al. (2003) and between chosen according to the Fe–S phase diagram (Narazawa and 1.6 GPa and 6.2 GPa according to Gilder et al. (2011). This pressure- Morimoto, 1971). Sometimes the capsules were taken out of the induced transition was the subject of previous studies that furnace and shaken to minimize agglomeration. Finally, the employed uniaxial press combined with a solid confining media, ampoules were extracted from the furnace and cooled in air. The resulting in quasi-hydrostatic compression (Rochette et al., 2003; mixture of salt and iron sulfide was progressively dissolved first Gilder et al., 2011; note that the neutron experiment in Rochette in distilled water, then in alcohol and finally in acetone using an et al. (2003) was using liquid confining media). It has subsequently ultrasonic cleaner. The final product was dried in a muffle furnace been suggested that purely hydrostatic conditions may be a better at 343 K for 5 min. analog for natural in situ conditions in the deep crust (Demory Further details on this synthesis procedure can be found in et al., 2013). (Chareev et al., 2014), which describes synthesis and investigations Despite these earlier studies characterizing the magnetic prop- of monoclinic pyrrhotite in equilibrium with pyrite (FeS2) in the erties of natural pyrrhotite, there are still many unanswered ques- Ag–Fe–S system. tions regarding the mechanisms by which magnetic remanence is To test the reproducibility of the method, we conducted three acquired by pyrrhotite. How does the underlying crystallography separate synthesis runs. Representative samples from
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