An X-ray magnetic circular dichroism (XMCD) study of Fe ordering in a synthetic MgAl2O4-Fe3O4(spinel-magnetite) solid-solution series: Implications for magnetic properties and cation site ordering

Henderson, C. M. B.; Pearce, Carolyn I.; Charnock, John; Harrison, R. J.; Rosso, Kevin M.

doi:10.2138/am-2016-5612

Cited by 12 publications

(10 citation statements)

References 77 publications

(105 reference statements)

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“…This was not observed in any samples we studied under microscope. By contrast, the spatial scale of the protonuclei described by Henderson et al (2016) is estimated to be <100 Å. Even when coarsened, they likely retain wavelengths far short of the well-developed texture observed by Price (1981a).…”

Section: Fine-scale Chemical Heterogeneitymentioning

confidence: 83%

“…The location of the first prominent peak in the near‐edge Mg XAS data increases from ~1,309 eV for tetrahedral coordination to ~1,311 eV for octahedral coordination (Ildefonse et al, ). Further, the relative height of the first two peaks shifts with increasing coordination from a more prominent first peak to a more prominent second peak (Henderson et al, ). Mg XAS data for our samples (Figure S10) show a relatively small less prominent first peak at ~1,311 eV, consistent with Mg in octahedral coordination.…”

Section: Resultsmentioning

confidence: 99%

“…Nanoscale chemical clustering, with eventual unmixing, is predicted for the MgFe 2 O 4 ‐Mg 2 TiO 4 system by atomistic modeling of cation ordering (Harrison et al, ). Henderson et al () used XMCD and XAS to study Fe ordering in synthetic MgAl 2 O 4 ‐Fe 3 O 4 solid solution samples. In the compositional range ~40–90% Fe 3 O 4 , they interpret the Fe XAS and XMCD data to represent nanoscale, Fe‐rich clusters.…”

Section: Discussionmentioning

confidence: 99%

“…Different cations have different octahedral site preference energy for placement in cubic spinels (Creer & Stephenson, 1972;Henderson et al, 2016;Lavina et al, 2002;Miller, 1959;Navrotsky & Kleppa, 1967). The resulting segregation will depend on the neighboring cations, and it remains incompletely understood in impure TMs.…”

Section: Tms Containing Al and Mgmentioning

confidence: 99%

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

Bowles

Lappe

Jackson

et al. 2019

Geochem Geophys Geosyst

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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.

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Section: Fine-scale Chemical Heterogeneitymentioning

confidence: 83%

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Tms Containing Al and Mgmentioning

confidence: 99%

See 2 more Smart Citations

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

Bowles

Lappe

Jackson

et al. 2019

Geochem Geophys Geosyst

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“…The structure of jacobsite, galaxite, and other oxide minerals with a spinel structure, consists of oxygen atoms arranged in a cubic close packed (ccp) structure, with cations filling ⅛ of the tetrahedral ( T ) and ½ of the octahedral ( M ) sites. An excess of metal cations will occupy normally vacant interstitial sites (Fleet 1981; Henderson et al ., 2016). The typical space group symmetry of spinels is Fd m .…”

Section: Introductionmentioning

confidence: 99%

Cation distribution and valence in synthetic Al–Mn–O and Fe–Mn–O spinels under varying conditions

et al. 2018

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The spinel-group minerals, found in a range of igneous rocks, are resistant to weathering and can incorporate several multivalent elements, meaning they have the potential to provide insight into the redox conditions of parental magmas. Naturally occurring spinel can contain varying quantities of Mn, an element which occurs terrestrially and extra-terrestrially as Mn 2+ , Mn 3+ , Mn 4+ and Mn 5+ . However, a lack of information on the effects of oxygen fugacity (f O 2 ) on: (1) Mn valence state and cation distribution; and (2) on spinel-melt partitioning means that the potential for a Mn-in-spinel oxy-barometer remains largely untested. Here, we use electron probe microanalysis, micro-focus X-ray Absorption Near Edge Structure (XANES) spectroscopy and single-crystal X-ray diffraction (SC-XRD) to investigate cation distribution and valence state in spinels in the Al-Mn-O and Fe-Mn-O systems synthesized at ambient pressure under varying f O 2 conditions. In contrast to previous studies, we find that the spectral resolution of the Mn K-edge XANES spectra is insufficient to provide quantitative data on Mn valence state and site occupancy, although it does verify that Mn is incorporated as both Mn 2+ and Mn 3+ , distributed over tetrahedral and octahedral sites. Combination of data from XANES and SC-XRD refinements can, however, be used to model Mn, Al and Fe valence and site occupancy. It would be expected that Mn-Fe spinels have the potential to record f O 2 conditions in parental melts due to changes to the octahedral site under conditions that were more reducing. However, decoupling the effects of temperature and oxygen fugacity on the T Fe 3+ -T Mn 2+ exchange in the Mn-Fe spinels remains challenging. In contrast, little variation is noted in Mn-Al spinels as a function of f O 2 , implying that crystal chemistry and cation site geometry may significantly influence cation distribution, and by inference, crystal-melt partitioning, in spinel-group minerals.K E Y WO R D S : spinel, manganese, XANES, oxygen fugacity, jacobsite, galaxite.

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Nanogeochemistry of hydrothermal magnetite

Deditius

Reich

Simon

et al. 2018

Contrib Mineral Petrol

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An X-ray magnetic circular dichroism (XMCD) study of Fe ordering in a synthetic MgAl₂O₄-Fe₃O₄(spinel-magnetite) solid-solution series: Implications for magnetic properties and cation site ordering

Abstract: An X-ray magnetic circular dichroism (XMCD) study of Fe ordering in a synthetic MgAl 2 O 4-Fe 3 O 4 (spinel-magnetite) solid solution series; implications for magnetic properties.

Cited by 12 publications

References 77 publications

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

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

Cation distribution and valence in synthetic Al–Mn–O and Fe–Mn–O spinels under varying conditions

Nanogeochemistry of hydrothermal magnetite

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