Morin-type transition in 5C pyrrhotite

Haines, C. R. Sebastian, Lampronti, Giulio I., Klooster, Wim, Coles, Simon J., Dutton, Sian E. and Carpenter, Michael A. (2020) Morin-type transition in 5C pyrrhotite. American Mineralogist, 105 (9). pp. 1404-1411. ISSN 0003-004X

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Abstract

We report the discovery of a low-temperature spin-flop transition in 5C pyrrhotite at ~155 K that is similar to those seen in hematite at 260 K and FeS (troilite) at 440 K. The 5C crystal was produced by annealing a 4C pyrrhotite crystal at 875 K to produce a change in the vacancy-ordering scheme that developed during cooling. The 5C structure is confirmed by single-crystal X-ray diffraction and the stoichiometry and homogeneity by electron microprobe and SEM BSE mapping. Resonant ultrasound spectroscopy (RUS), heat capacity, and magnetization measurements from room temperature down to 2 K are reported. The transition is marked by a steep change in elastic properties at the transition temperature, a peak in the heat capacity, and weak anomalies in measurements of magnetization. Magnetic hysteresis loops and comparison with the magnetic properties of 4C pyrrhotite suggest that the transition involves a change in orientation of moments between two different antiferromagnetic structures, perpendicular to the crystallographic c-axis at high temperatures and parallel to the crystallographic c-axis at low temperatures. The proposed structures are consistent with a group theoretical treatment that also predicts a first-order transition between the magnetic structures.

Item Type: Article
Additional Information: Funding Information: The authors acknowledge funding from the Leverhulme Foundation, grant number RPG2016-298. Heat capacity and DC magnetic measurements were carried out using the Advanced Materials Characterization Suite, funded by EPSRC Strategic Equipment Grant EP/M000524/1. RUS facilities in Cambridge were funded by grants to MAC from the Natural Environment Research Council of Great Britain (grant nos. NE/B505738/1 and NE/F17081/1) and from the Engineering and Physical Sciences Research Council (grant no. EP/I036079/1).
Uncontrolled Keywords: crystal structure,mineralogy,palaeomagnetism,pyrrhotite,geophysics,geochemistry and petrology ,/dk/atira/pure/subjectarea/asjc/1900/1908
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Depositing User: LivePure Connector
Date Deposited: 27 Oct 2021 02:24
Last Modified: 02 Nov 2021 01:58
URI: https://ueaeprints.uea.ac.uk/id/eprint/81889
DOI: 10.2138/am-2020-7266

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