Magnetic domain state and anisotropy in monoclinic 4C pyrrhotite (Fe₇S₈) from first-order reversal curve diagrams
File(s)
Accepted version
Author(s)
Type
Journal Article
Abstract
First-order reversal curve (FORC) diagrams are an important tool for assessing the domain state and anisotropy type of magnetic particles, as well as for detecting magnetostatic interactions among particles, in paleoclimatic, geomagnetic, tectonic, and planetary studies. We present here FORC diagrams for diverse natural monoclinic 4C pyrrhotite (Fe7S8) samples, including sieved particle size fractions. Experimental FORC distributions for natural pyrrhotite have a dominant asymmetric “kidney shaped” feature for fine particles in the stable single domain (SD) size range. As particles coarsen to the multi-domain state, FORC distributions diverge vertically at low coercivities. Vertical spreading in FORC distributions is also an intrinsic response of magnetic particle systems with multiaxial anisotropy even for magnetostatically noninteracting SD particles. The observed kidney shaped FORC distributions are attributed to twin domain and magnetic moment pinning along easy directions that follow the hexagonal parent structure to produce an apparent triaxial magnetocrystalline anisotropy signal. Similar FORC distributions have been reported for pyrrhotite, hematite, and smythite, which all have basal plane triaxial anisotropy. Central ridge-type signatures, which are typical of noninteracting uniaxial SD particle assemblages, have been reported for some pyrrhotite samples, but are not documented here. Our results explain FORC features for pyrrhotite and provide a catalog for comparison with other studies.
Date Issued
2026-02-01
Date Acceptance
2025-12-20
Citation
Journal of Geophysical Research (JGR): Solid Earth, 2026, 131 (2)
ISSN
2169-9313
Publisher
American Geophysical Union
Journal / Book Title
Journal of Geophysical Research (JGR): Solid Earth
Volume
131
Issue
2
Copyright Statement
Copyright © 2026. American Geophysical Union. This is the author’s accepted manuscript made available under a CC-BY licence in accordance with Imperial’s Research Publications Open Access policy (www.imperial.ac.uk/oa-policy)
License URL
Publication Status
Published
Article Number
e2025JB032900
Date Publish Online
2026-02-12