Curie Temperature Enhancement and Cation Ordering in Titanomagnetites: Evidence From Magnetic Properties, XMCD, and Mössbauer Spectroscopy

J. A. Bowles; S. C.L.L. Lappe; M. J. Jackson; E. Arenholz; G. van der Laan

doi:10.1029/2019GC008217

Curie Temperature Enhancement and Cation Ordering in Titanomagnetites: Evidence From Magnetic Properties, XMCD, and Mössbauer Spectroscopy

J. A. Bowles, S. C.L.L. Lappe, M. J. Jackson, E. Arenholz, G. van der Laan

Earth and Environmental Sciences-Twin Cities

Research output: Contribution to journal › Article › peer-review

5 Scopus citations

Abstract

Previous work has documented time- and temperature-dependent variations in the Curie temperature (T_c) of natural titanomagnetites, independent of any changes in sample composition. To better understand the atomic-scale processes responsible for these variations, we have generated a set of synthetic titanomagnetites with a range of Ti, Mg, and Al substitution; a subset of samples was additionally oxidized at low temperature (150 °C). Samples were annealed at temperatures between 325 and 400 °C for up to 1,000 hr and characterized in terms of magnetic properties; Fe valence and site occupancy were constrained by X-ray magnetic circular dichroism (XMCD) and Mössbauer spectroscopy. Annealing results in large (up to ~100 °C) changes in T_c, but Mössbauer, XMCD, and saturation magnetization data all demonstrate that intersite reordering of Fe²⁺/Fe³⁺ does not play a role in the observed T_c changes. Rather, the data are consistent with vacancy-enhanced nanoscale chemical clustering within the octahedral sublattice. This clustering may be a precursor to chemical unmixing at temperatures below the titanomagnetite binary solvus. Additionally, the data strongly support a model where cation vacancies are predominantly situated on octahedral sites, Mg substitution is largely accommodated on octahedral sites, and Al substitution is split between the two sites.

Original language	English (US)
Pages (from-to)	2272-2289
Number of pages	18
Journal	Geochemistry, Geophysics, Geosystems
Volume	20
Issue number	5
DOIs	https://doi.org/10.1029/2019GC008217
State	Published - May 2019

Bibliographical note

Funding Information:
We thank Richard Pattrick and Carolyn Pearce for advice and assistance with our initial XMCD studies, and David Keavney for beamline support and advice at APS. We thank Bruce Moskowitz and Peat Sølheid for helpful discussions on Mössbauer analysis, Lindsay McHenry for assistance with XRD measurements, and John Fournelle for microprobe preparation and measurements. Many thanks to reviewers Richard Harrison and Dominique Lattard for their thoughtful and helpful comments that improved the manuscript. This research used resources of the Advanced Light Source (ALS) and the Advanced Photon Source (APS). ALS is a U.S. Department of Energy (DOE) Office of Science User Facility under contract DE‐AC02‐ 05CH11231. APS is a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract DE‐AC02‐06CH11357. This research was made possible by NSF grants EAR1315971 to J. A. B. and EAR1315845 to M. J. J., as well as access to the Institute for Rock Magnetism, which is supported by the NSF Instruments and Facilities program and by the University of Minnesota. This is IRM contribution #1815. Magnetic data associated with this manuscript are available from the Magnetics Information Consortium (MagIC) database at the website (https:// earthref.org/MagIC/doi/10.1029/ 2019GC008217).

Funding Information:
We thank Richard Pattrick and Carolyn Pearce for advice and assistance with our initial XMCD studies, and David Keavney for beamline support and advice at APS. We thank Bruce Moskowitz and Peat S?lheid for helpful discussions on M?ssbauer analysis, Lindsay McHenry for assistance with XRD measurements, and John Fournelle for microprobe preparation and measurements. Many thanks to reviewers Richard Harrison and Dominique Lattard for their thoughtful and helpful comments that improved the manuscript. This research used resources of the Advanced Light Source (ALS) and the Advanced Photon Source (APS). ALS is a U.S. Department of Energy (DOE) Office of Science User Facility under contract DE-AC02-05CH11231. APS is a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract DE-AC02-06CH11357. This research was made possible by NSF grants EAR1315971 to J.?A.?B. and EAR1315845 to M.?J.?J., as well as access to the Institute for Rock Magnetism, which is supported by the NSF Instruments and Facilities program and by the University of Minnesota. This is IRM contribution #1815. Magnetic data associated with this manuscript are available from the Magnetics Information Consortium (MagIC) database at the website (https://earthref.org/MagIC/doi/10.1029/2019GC008217).

Publisher Copyright:
©2019. American Geophysical Union. All Rights Reserved.

Keywords

Curie temperature
Mossbauer
XMCD
cation ordering
mineral magnetism
titanomagnetite

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10.1029/2019GC008217

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title = "Curie Temperature Enhancement and Cation Ordering in Titanomagnetites: Evidence From Magnetic Properties, XMCD, and M{\"o}ssbauer Spectroscopy",

abstract = "Previous work has documented time- and temperature-dependent variations in the Curie temperature (Tc) of natural titanomagnetites, independent of any changes in sample composition. To better understand the atomic-scale processes responsible for these variations, we have generated a set of synthetic titanomagnetites with a range of Ti, Mg, and Al substitution; a subset of samples was additionally oxidized at low temperature (150 °C). Samples were annealed at temperatures between 325 and 400 °C for up to 1,000 hr and characterized in terms of magnetic properties; Fe valence and site occupancy were constrained by X-ray magnetic circular dichroism (XMCD) and M{\"o}ssbauer spectroscopy. Annealing results in large (up to ~100 °C) changes in Tc, but M{\"o}ssbauer, XMCD, and saturation magnetization data all demonstrate that intersite reordering of Fe2+/Fe3+ does not play a role in the observed Tc changes. Rather, the data are consistent with vacancy-enhanced nanoscale chemical clustering within the octahedral sublattice. This clustering may be a precursor to chemical unmixing at temperatures below the titanomagnetite binary solvus. Additionally, the data strongly support a model where cation vacancies are predominantly situated on octahedral sites, Mg substitution is largely accommodated on octahedral sites, and Al substitution is split between the two sites.",

keywords = "Curie temperature, Mossbauer, XMCD, cation ordering, mineral magnetism, titanomagnetite",

author = "Bowles, {J. A.} and Lappe, {S. C.L.L.} and Jackson, {M. J.} and E. Arenholz and {van der Laan}, G.",

note = "Funding Information: We thank Richard Pattrick and Carolyn Pearce for advice and assistance with our initial XMCD studies, and David Keavney for beamline support and advice at APS. We thank Bruce Moskowitz and Peat S{\o}lheid for helpful discussions on M{\"o}ssbauer analysis, Lindsay McHenry for assistance with XRD measurements, and John Fournelle for microprobe preparation and measurements. Many thanks to reviewers Richard Harrison and Dominique Lattard for their thoughtful and helpful comments that improved the manuscript. This research used resources of the Advanced Light Source (ALS) and the Advanced Photon Source (APS). ALS is a U.S. Department of Energy (DOE) Office of Science User Facility under contract DE‐AC02‐ 05CH11231. APS is a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract DE‐AC02‐06CH11357. This research was made possible by NSF grants EAR1315971 to J. A. B. and EAR1315845 to M. J. J., as well as access to the Institute for Rock Magnetism, which is supported by the NSF Instruments and Facilities program and by the University of Minnesota. This is IRM contribution #1815. Magnetic data associated with this manuscript are available from the Magnetics Information Consortium (MagIC) database at the website (https:// earthref.org/MagIC/doi/10.1029/ 2019GC008217). Funding Information: We thank Richard Pattrick and Carolyn Pearce for advice and assistance with our initial XMCD studies, and David Keavney for beamline support and advice at APS. We thank Bruce Moskowitz and Peat S?lheid for helpful discussions on M?ssbauer analysis, Lindsay McHenry for assistance with XRD measurements, and John Fournelle for microprobe preparation and measurements. Many thanks to reviewers Richard Harrison and Dominique Lattard for their thoughtful and helpful comments that improved the manuscript. This research used resources of the Advanced Light Source (ALS) and the Advanced Photon Source (APS). ALS is a U.S. Department of Energy (DOE) Office of Science User Facility under contract DE-AC02-05CH11231. APS is a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract DE-AC02-06CH11357. This research was made possible by NSF grants EAR1315971 to J.?A.?B. and EAR1315845 to M.?J.?J., as well as access to the Institute for Rock Magnetism, which is supported by the NSF Instruments and Facilities program and by the University of Minnesota. This is IRM contribution #1815. Magnetic data associated with this manuscript are available from the Magnetics Information Consortium (MagIC) database at the website (https://earthref.org/MagIC/doi/10.1029/2019GC008217). Publisher Copyright: {\textcopyright}2019. American Geophysical Union. All Rights Reserved.",

year = "2019",

month = may,

doi = "10.1029/2019GC008217",

language = "English (US)",

volume = "20",

pages = "2272--2289",

journal = "Geochemistry, Geophysics, Geosystems",

issn = "1525-2027",

publisher = "American Geophysical Union",

number = "5",

}

TY - JOUR

T1 - Curie Temperature Enhancement and Cation Ordering in Titanomagnetites

T2 - Evidence From Magnetic Properties, XMCD, and Mössbauer Spectroscopy

AU - Bowles, J. A.

AU - Lappe, S. C.L.L.

AU - Jackson, M. J.

AU - Arenholz, E.

AU - van der Laan, G.

N1 - Funding Information: We thank Richard Pattrick and Carolyn Pearce for advice and assistance with our initial XMCD studies, and David Keavney for beamline support and advice at APS. We thank Bruce Moskowitz and Peat Sølheid for helpful discussions on Mössbauer analysis, Lindsay McHenry for assistance with XRD measurements, and John Fournelle for microprobe preparation and measurements. Many thanks to reviewers Richard Harrison and Dominique Lattard for their thoughtful and helpful comments that improved the manuscript. This research used resources of the Advanced Light Source (ALS) and the Advanced Photon Source (APS). ALS is a U.S. Department of Energy (DOE) Office of Science User Facility under contract DE‐AC02‐ 05CH11231. APS is a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract DE‐AC02‐06CH11357. This research was made possible by NSF grants EAR1315971 to J. A. B. and EAR1315845 to M. J. J., as well as access to the Institute for Rock Magnetism, which is supported by the NSF Instruments and Facilities program and by the University of Minnesota. This is IRM contribution #1815. Magnetic data associated with this manuscript are available from the Magnetics Information Consortium (MagIC) database at the website (https:// earthref.org/MagIC/doi/10.1029/ 2019GC008217). Funding Information: We thank Richard Pattrick and Carolyn Pearce for advice and assistance with our initial XMCD studies, and David Keavney for beamline support and advice at APS. We thank Bruce Moskowitz and Peat S?lheid for helpful discussions on M?ssbauer analysis, Lindsay McHenry for assistance with XRD measurements, and John Fournelle for microprobe preparation and measurements. Many thanks to reviewers Richard Harrison and Dominique Lattard for their thoughtful and helpful comments that improved the manuscript. This research used resources of the Advanced Light Source (ALS) and the Advanced Photon Source (APS). ALS is a U.S. Department of Energy (DOE) Office of Science User Facility under contract DE-AC02-05CH11231. APS is a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract DE-AC02-06CH11357. This research was made possible by NSF grants EAR1315971 to J.?A.?B. and EAR1315845 to M.?J.?J., as well as access to the Institute for Rock Magnetism, which is supported by the NSF Instruments and Facilities program and by the University of Minnesota. This is IRM contribution #1815. Magnetic data associated with this manuscript are available from the Magnetics Information Consortium (MagIC) database at the website (https://earthref.org/MagIC/doi/10.1029/2019GC008217). Publisher Copyright: ©2019. American Geophysical Union. All Rights Reserved.

PY - 2019/5

Y1 - 2019/5

N2 - Previous work has documented time- and temperature-dependent variations in the Curie temperature (Tc) of natural titanomagnetites, independent of any changes in sample composition. To better understand the atomic-scale processes responsible for these variations, we have generated a set of synthetic titanomagnetites with a range of Ti, Mg, and Al substitution; a subset of samples was additionally oxidized at low temperature (150 °C). Samples were annealed at temperatures between 325 and 400 °C for up to 1,000 hr and characterized in terms of magnetic properties; Fe valence and site occupancy were constrained by X-ray magnetic circular dichroism (XMCD) and Mössbauer spectroscopy. Annealing results in large (up to ~100 °C) changes in Tc, but Mössbauer, XMCD, and saturation magnetization data all demonstrate that intersite reordering of Fe2+/Fe3+ does not play a role in the observed Tc changes. Rather, the data are consistent with vacancy-enhanced nanoscale chemical clustering within the octahedral sublattice. This clustering may be a precursor to chemical unmixing at temperatures below the titanomagnetite binary solvus. Additionally, the data strongly support a model where cation vacancies are predominantly situated on octahedral sites, Mg substitution is largely accommodated on octahedral sites, and Al substitution is split between the two sites.

AB - Previous work has documented time- and temperature-dependent variations in the Curie temperature (Tc) of natural titanomagnetites, independent of any changes in sample composition. To better understand the atomic-scale processes responsible for these variations, we have generated a set of synthetic titanomagnetites with a range of Ti, Mg, and Al substitution; a subset of samples was additionally oxidized at low temperature (150 °C). Samples were annealed at temperatures between 325 and 400 °C for up to 1,000 hr and characterized in terms of magnetic properties; Fe valence and site occupancy were constrained by X-ray magnetic circular dichroism (XMCD) and Mössbauer spectroscopy. Annealing results in large (up to ~100 °C) changes in Tc, but Mössbauer, XMCD, and saturation magnetization data all demonstrate that intersite reordering of Fe2+/Fe3+ does not play a role in the observed Tc changes. Rather, the data are consistent with vacancy-enhanced nanoscale chemical clustering within the octahedral sublattice. This clustering may be a precursor to chemical unmixing at temperatures below the titanomagnetite binary solvus. Additionally, the data strongly support a model where cation vacancies are predominantly situated on octahedral sites, Mg substitution is largely accommodated on octahedral sites, and Al substitution is split between the two sites.

KW - Curie temperature

KW - Mossbauer

KW - XMCD

KW - cation ordering

KW - mineral magnetism

KW - titanomagnetite

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VL - 20

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JO - Geochemistry, Geophysics, Geosystems

JF - Geochemistry, Geophysics, Geosystems

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ER -

Curie Temperature Enhancement and Cation Ordering in Titanomagnetites: Evidence From Magnetic Properties, XMCD, and Mössbauer Spectroscopy

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