Morin-type transition in 5C pyrrhotite

C. R. Sebastian Haines, Giulio I. Lampronti, Wim Klooster, Simon J. Coles, Sian E. Dutton, Michael A. Carpenter

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Pages (from-to)1404-1411
Number of pages8
JournalAmerican Mineralogist
Issue number9
Early online date20 Sep 2020
Publication statusPublished - 25 Sep 2020


  • Crystal structure
  • Mineralogy
  • Palaeomagnetism
  • Pyrrhotite

Cite this