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Morin-type transition in 5C pyrrhotite

Morin-type transition in 5C pyrrhotite
Morin-type transition in 5C pyrrhotite
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 crystal-lographic 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.
Morin-type transfers, annealing, crystal structure, experimental studies, laboratory studies, magnetic hysteresis, magnetic properties, paleomagnetism, phase transitions, polymorphism, stoichiometry, sulfides, troilite
0003-004X
1404-1411
Haines, Charles R.S.
88208ca0-857f-4ba2-a6da-07cd288b44ec
Lampronti, Giulio I.
214c586a-61fb-455d-802d-b95d3136b9c8
Klooster, Wim
64dc0111-f415-4226-9189-45764c0933d9
Coles, Simon J.
3116f58b-c30c-48cf-bdd5-397d1c1fecf8
Dutton, Sian E.
944988b6-72db-46e8-b134-9a072e9def1c
Carpenter, Michael A.
f315cc37-0eed-4093-a125-75e78215c46b
Haines, Charles R.S.
88208ca0-857f-4ba2-a6da-07cd288b44ec
Lampronti, Giulio I.
214c586a-61fb-455d-802d-b95d3136b9c8
Klooster, Wim
64dc0111-f415-4226-9189-45764c0933d9
Coles, Simon J.
3116f58b-c30c-48cf-bdd5-397d1c1fecf8
Dutton, Sian E.
944988b6-72db-46e8-b134-9a072e9def1c
Carpenter, Michael A.
f315cc37-0eed-4093-a125-75e78215c46b

Haines, Charles R.S., 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), 1404-1411. (doi:10.2138/am-2020-7266).

Record type: Article

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 crystal-lographic 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.

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Accepted/In Press date: 26 February 2020
e-pub ahead of print date: 1 September 2020
Published date: 25 September 2020
Keywords: Morin-type transfers, annealing, crystal structure, experimental studies, laboratory studies, magnetic hysteresis, magnetic properties, paleomagnetism, phase transitions, polymorphism, stoichiometry, sulfides, troilite

Identifiers

Local EPrints ID: 445190
URI: http://eprints.soton.ac.uk/id/eprint/445190
ISSN: 0003-004X
PURE UUID: b0980a42-4d3a-4058-a8a0-692a28d7b217
ORCID for Simon J. Coles: ORCID iD orcid.org/0000-0001-8414-9272

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Date deposited: 25 Nov 2020 17:30
Last modified: 26 Nov 2021 05:58

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Contributors

Author: Charles R.S. Haines
Author: Giulio I. Lampronti
Author: Wim Klooster
Author: Simon J. Coles ORCID iD
Author: Sian E. Dutton
Author: Michael A. Carpenter

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