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Licensed Unlicensed Requires Authentication Published by De Gruyter September 20, 2020

Morin-type transition in 5C pyrrhotite

  • Charles R.S. Haines ORCID logo , Giulio I. Lampronti , Wim T. Klooster , Simon J. Coles , Sian E. Dutton and Michael A. Carpenter
From the journal American Mineralogist


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.

  1. Funding

    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).

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Received: 2019-08-20
Accepted: 2020-02-26
Published Online: 2020-09-20
Published in Print: 2020-09-25

© 2020 Walter de Gruyter GmbH, Berlin/Boston

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