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Magnetic properties of sedimentary greigite (Fe3S4): An update

Magnetic properties of sedimentary greigite (Fe3S4): An update
Magnetic properties of sedimentary greigite (Fe3S4): An update
Greigite (Fe3S4) is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction. It can also grow at any time when dissolved iron and sulfide are available during diagenesis. Greigite is important in paleomagnetic, environmental, biological, biogeochemical, tectonic, and industrial processes. Much recent progress has been made in understanding its magnetic properties. Greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites. The crystallographic c axis is the easy axis of magnetization, with magnetic properties dominated by magnetocrystalline anisotropy. Robust empirical estimates of the saturation magnetization, anisotropy constant, and exchange constant for greigite have been obtained recently for the first time, and the first robust estimate of the low-field magnetic susceptibility is reported here. The Curie temperature of greigite remains unknown but must exceed 350°C. Greigite lacks a low-temperature magnetic transition. On the basis of preliminary micromagnetic modeling, the size range for stable single domain behavior is 17–200 nm for cubic crystals and 17–500 nm for octahedral crystals. Gradual variation in magnetic properties is observed through the pseudo-single-domain size range. We systematically document the known magnetic properties of greigite (at high, ambient, and low temperatures and with alternating and direct fields) and illustrate how grain size variations affect magnetic properties. Recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite, which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records, including widespread remagnetizations.
RG1002
Roberts, Andrew P.
4f062491-5408-4edb-8dd1-140c6a42e93f
Chang, Liao
83123f49-dd71-43a9-a0b1-d80777231b44
Rowan, Christopher J.
c90b0a90-bdeb-4485-81dc-af73e5501165
Horng, Chorng-Shern
3d0d9429-844f-4f37-9a02-ccd2be8df121
Florindo, Fabio
5953170b-79f7-431e-9e08-824a47e0fbd5
Roberts, Andrew P.
4f062491-5408-4edb-8dd1-140c6a42e93f
Chang, Liao
83123f49-dd71-43a9-a0b1-d80777231b44
Rowan, Christopher J.
c90b0a90-bdeb-4485-81dc-af73e5501165
Horng, Chorng-Shern
3d0d9429-844f-4f37-9a02-ccd2be8df121
Florindo, Fabio
5953170b-79f7-431e-9e08-824a47e0fbd5

Roberts, Andrew P., Chang, Liao, Rowan, Christopher J., Horng, Chorng-Shern and Florindo, Fabio (2011) Magnetic properties of sedimentary greigite (Fe3S4): An update. Reviews of Geophysics, 49 (1), RG1002. (doi:10.1029/2010RG000336).

Record type: Article

Abstract

Greigite (Fe3S4) is an authigenic ferrimagnetic mineral that grows as a precursor to pyrite during early diagenetic sedimentary sulfate reduction. It can also grow at any time when dissolved iron and sulfide are available during diagenesis. Greigite is important in paleomagnetic, environmental, biological, biogeochemical, tectonic, and industrial processes. Much recent progress has been made in understanding its magnetic properties. Greigite is an inverse spinel and a collinear ferrimagnet with antiferromagnetic coupling between iron in octahedral and tetrahedral sites. The crystallographic c axis is the easy axis of magnetization, with magnetic properties dominated by magnetocrystalline anisotropy. Robust empirical estimates of the saturation magnetization, anisotropy constant, and exchange constant for greigite have been obtained recently for the first time, and the first robust estimate of the low-field magnetic susceptibility is reported here. The Curie temperature of greigite remains unknown but must exceed 350°C. Greigite lacks a low-temperature magnetic transition. On the basis of preliminary micromagnetic modeling, the size range for stable single domain behavior is 17–200 nm for cubic crystals and 17–500 nm for octahedral crystals. Gradual variation in magnetic properties is observed through the pseudo-single-domain size range. We systematically document the known magnetic properties of greigite (at high, ambient, and low temperatures and with alternating and direct fields) and illustrate how grain size variations affect magnetic properties. Recognition of this range of magnetic properties will aid identification and constrain interpretation of magnetic signals carried by greigite, which is increasingly proving to be environmentally important and responsible for complex paleomagnetic records, including widespread remagnetizations.

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Published date: 29 January 2011
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 176545
URI: http://eprints.soton.ac.uk/id/eprint/176545
PURE UUID: 2441d7c1-e8ed-4a5d-9c0d-84a5c79cbf83

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Date deposited: 08 Mar 2011 11:35
Last modified: 08 Nov 2021 18:59

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Contributors

Author: Andrew P. Roberts
Author: Liao Chang
Author: Christopher J. Rowan
Author: Chorng-Shern Horng
Author: Fabio Florindo

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