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Fundamental magnetic parameters from pure synthetic greigite (Fe3S4)

Fundamental magnetic parameters from pure synthetic greigite (Fe3S4)
Fundamental magnetic parameters from pure synthetic greigite (Fe3S4)
Pure ferrimagnetic greigite (Fe3S4) has been synthesized by reacting ferric chloride with thiourea and formic acid at 170°C. Sample purity was confirmed by X-ray diffraction, neutron diffraction and Mössbauer spectroscopy, coupled with magnetic measurements. Scanning electron microscope observations indicate clear cubo-octahedral and polyhedral crystal morphologies. The grain sizes are as large as 44 ?m. Detailed low- and high-temperature magnetic measurements document the previously poorly known magnetic properties of greigite. The synthetic greigite samples are dominated by pseudo-single-domain and multi-domain behavior. The saturation magnetization (M s ) at room temperature is ?59 Am2kg?1 (3.13 ? B per formula unit), which is higher than any value previously reported for greigite in the literature largely because of the high purity of this sample compared to others. No low-temperature magnetic transition has been detected; however, a local coercivity minimum is observed at around 130 K, which is probably associated with domain walls present in the studied samples. The high-temperature magnetic properties of greigite are dominated by chemical decomposition above around 250°C, which precludes determination of the Curie temperature, but our evidence indicates that it must exceed 350°C. On the basis of the Bloch spin wave expansion, the spin wave stiffness of greigite was determined for the first time as ?193 meV·Å2 from low-temperature M s measurements, with the corresponding exchange constant J AB of ?1.03 meV.
Greigite, synthesis, magnetic properties, saturation magnetization, exchange constant, Curie temperature, Mössbauer spectroscopy
0148-0227
B06104
Chang, L.
d6c90fb1-6a1c-4ac0-9b98-8556d2e80d4c
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52
Tang, Y.
e1d9ef8e-9e0a-49d3-b0a8-e572f8298c47
Chen, Q.W.
8309d1fc-24be-49ce-b5c5-cfa2bc2562aa
Rainford, B.D.
0fdf537e-369d-46b4-98f2-b4f1812ca1aa
Muxworthy, A.R.
931b5755-e923-4995-957f-6af47c5ba6b4
Chang, L.
d6c90fb1-6a1c-4ac0-9b98-8556d2e80d4c
Roberts, A.P.
4497b436-ef02-428d-a46e-65a22094ba52
Tang, Y.
e1d9ef8e-9e0a-49d3-b0a8-e572f8298c47
Chen, Q.W.
8309d1fc-24be-49ce-b5c5-cfa2bc2562aa
Rainford, B.D.
0fdf537e-369d-46b4-98f2-b4f1812ca1aa
Muxworthy, A.R.
931b5755-e923-4995-957f-6af47c5ba6b4

Chang, L., Roberts, A.P., Tang, Y., Chen, Q.W., Rainford, B.D. and Muxworthy, A.R. (2008) Fundamental magnetic parameters from pure synthetic greigite (Fe3S4). Journal of Geophysical Research, 113, B06104. (doi:10.1029/2007JB005502).

Record type: Article

Abstract

Pure ferrimagnetic greigite (Fe3S4) has been synthesized by reacting ferric chloride with thiourea and formic acid at 170°C. Sample purity was confirmed by X-ray diffraction, neutron diffraction and Mössbauer spectroscopy, coupled with magnetic measurements. Scanning electron microscope observations indicate clear cubo-octahedral and polyhedral crystal morphologies. The grain sizes are as large as 44 ?m. Detailed low- and high-temperature magnetic measurements document the previously poorly known magnetic properties of greigite. The synthetic greigite samples are dominated by pseudo-single-domain and multi-domain behavior. The saturation magnetization (M s ) at room temperature is ?59 Am2kg?1 (3.13 ? B per formula unit), which is higher than any value previously reported for greigite in the literature largely because of the high purity of this sample compared to others. No low-temperature magnetic transition has been detected; however, a local coercivity minimum is observed at around 130 K, which is probably associated with domain walls present in the studied samples. The high-temperature magnetic properties of greigite are dominated by chemical decomposition above around 250°C, which precludes determination of the Curie temperature, but our evidence indicates that it must exceed 350°C. On the basis of the Bloch spin wave expansion, the spin wave stiffness of greigite was determined for the first time as ?193 meV·Å2 from low-temperature M s measurements, with the corresponding exchange constant J AB of ?1.03 meV.

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Published date: 2008
Keywords: Greigite, synthesis, magnetic properties, saturation magnetization, exchange constant, Curie temperature, Mössbauer spectroscopy

Identifiers

Local EPrints ID: 54783
URI: https://eprints.soton.ac.uk/id/eprint/54783
ISSN: 0148-0227
PURE UUID: 81064122-e194-4772-8bc8-8a86cbbcde27

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Date deposited: 21 Jul 2008
Last modified: 13 Mar 2019 20:38

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Contributors

Author: L. Chang
Author: A.P. Roberts
Author: Y. Tang
Author: Q.W. Chen
Author: B.D. Rainford
Author: A.R. Muxworthy

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