Perturbation de l'echange electronique rapide par les lacunes cationiques dans Fe3−xO4(x ⩽ 0,09)

Ramdani, A.; Steinmetz, J.; Gleitzer, C.; Coey, J. M. D.; Friedt, J.M.

doi:10.1016/0022-3697(87)90016-3

Cited by 35 publications

(17 citation statements)

References 29 publications

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“…t 50 K, the L fraction spectra (Figure 8b) are typical of bulk nonstoichiometric magnetite (Daniels and Rosencwaig, 1969;Ramdani et al, 1987). Assuming identical recoilless fractions for all Fe ions at 4 K, the results of the fit (Table 3) Investigations of a fractionated suspension at x = 0.10 produced similar results.…”

Section: Clays and Clay Mineralssupporting

confidence: 71%

Influence of Fe(II) on the Formation of the Spinel Iron Oxide in Alkaline Medium

Jolivet

Belleville

Tronc

et al. 1992

Clays and clay miner.

132

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Fe(II) and Fe(III) in various proportions were coprecipitated by NH3 at pH ≈ 11. The Fe(II)/Fe(III) ratio (x) was varied from 0.10 to 0.50. After stabilization by aging at pH ≃ 8 in anaerobic conditions, hydrous precipitates were characterized by electron microscopy, Mössbauer spectroscopy, and kinetics of dissolution in acidic medium. At any x value, all stable products exhibited the structure of (oxidized) magnetite. For x ≤ 0.30, two distinct species were coexisting: the one (“m”) was made up of ca. 4nm-sized particles with a low Fe(II) content (Fe(II)/Fe(III) ≈ 0.07), and the other (“M”) consisted of particles of larger, more or less distributed sizes, and composition Fe(II)/Fe(III) ≈ 0.33; “M” increased relative amount with increasing x. For x ≥ 0.35, “M” was the only constituent and its Fe(II)/Fe(III) ratio was equal to x. “M” is identified with (nonstoichiometric) magnetite, whereas “m” is likely to be an oxyhydroxide. Mechanisms of formation are discussed, and a phase diagram is proposed which schematizes the evolution of the coprecipitation products with x and with time. Addition of Fe(II) after the precipitation of Fe(III), instead of coprecipitation, yielded very similar results.

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Section: Clays and Clay Mineralssupporting

confidence: 71%

Influence of Fe(II) on the Formation of the Spinel Iron Oxide in Alkaline Medium

Jolivet

Belleville

Tronc

et al. 1992

Clays and clay miner.

132

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“…F B /F A = relative area ratio of sextet B to sextet A. F B /F A is calculated assuming

true[{Fe}_{normalB}^{2 +} true] true[{Fe}_{normalA}^{3 +} {Fe}_{normalB}^{3 +} true]

. The estimate for z was made by comparing F B /F A ratios to those in the literature [ Ramdani et al ., ; Schmidbauer and Keller , ].…”

Section: Resultssupporting

confidence: 72%

Effect of maghemization on the magnetic properties of nonstoichiometric pseudo‐single‐domain magnetite particles

Almeida

Muxworthy

Kasama

et al. 2015

Geochem Geophys Geosyst

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The effect of maghemization on the magnetic properties of magnetite (Fe 3 O 4 ) grains in the pseudo-single-domain (PSD) size range is investigated as a function of annealing temperature. X-ray diffraction and transmission electron microscopy confirm the precursor grains as Fe 3 O 4 ranging from $150 to $250 nm in diameter, whilst M€ ossbauer spectrometry suggests the grains are initially near-stoichiometric. The Fe 3 O 4 grains are heated to increasing reaction temperatures of 120-2208C to investigate their oxidation to maghemite (c-Fe 2 O 3 ). High-angle annular dark field imaging and localized electron-energy loss spectroscopy reveal slightly oxidized Fe 3 O 4 grains, heated to 1408C, exhibit higher oxygen content at the surface. Off-axis electron holography allows for construction of magnetic induction maps of individual Fe 3 O 4 and cFe 2 O 3 grains, revealing their PSD (vortex) nature, which is supported by magnetic hysteresis measurements, including first-order reversal curve analysis. The coercivity of the grains is shown to increase with reaction temperature up to 1808C, but subsequently decreases after heating above 2008C; this magnetic behavior is attributed to the growth of a c-Fe 2 O 3 shell with magnetic properties distinct from the Fe 3 O 4 core. It is suggested there is exchange coupling between these separate components that results in a vortex state with reduced vorticity. Once fully oxidized to c-Fe 2 O 3 , the domain states revert back to vortices with slightly reduced coercivity. It is argued that due to a core/shell coupling mechanism during maghemization, the directional magnetic information will still be correct; however, the intensity information will not be retained.

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“…In contrast, a Mössbauer spectrum for RR (Figure 3) was complex displaying both a hematite phase and a nonstoichiometric maghemite/magnetite phase, as well as a small doublet. Using the cation deficient model given above it is possible to estimate the oxidation parameter z from the Mössbauer spectrum to be ∼0.5 [ Ramdani et al , 1987; Vandenberghe et al , 2000]. The area associated with the nonstoichiometric maghemite/magnetite phase was 59%, and 37% for hematite and 4% for the doublet.…”

Section: Sample Description and Experimental Methodsmentioning

confidence: 99%

Assessing the ability of first‐order reversal curve (FORC) diagrams to unravel complex magnetic signals

2005

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[1] First-order reversal curve (FORC) diagrams for mixtures of different magnetic phases and bimodal distributions have been measured to examine the efficiency of the FORC method at unraveling complex magnetic signals. The FORC distributions for various magnetic minerals, including magnetite, maghemite, hematite, and goethite, and their linear additivity are assessed. Mixtures containing only hard magnetic minerals like hematite or goethite, which have relatively small spontaneous magnetizations (M S ) and large magnetocrystalline anisotropies, can be adequately described by a linear addition of the two end-members, because there are virtually no magnetostatic interactions between the phases. Mixtures dominated by softer minerals like magnetite and maghemite are more susceptible to interactions and exhibit nonlinear behavior. When a hard phase with low M S like hematite is mixed with a softer phase with high M S like magnetite, it can still be identified using the FORC technique, whereas it is impossible to do so using standard magnetic hysteresis measurements. When the weaker phase can be identified, then weakstrong mixes add linearly; however, beyond a certain critical concentration the mineral with high M S swamps the magnetic signal and linearity breaks down. It is suggested that the FORC method is highly suitable for identifying small traces of hard magnetic minerals like hematite and goethite in the presence of minerals with high M S such as magnetite.Citation: Muxworthy, A. R., J. G. King, and D. Heslop (2005), Assessing the ability of first-order reversal curve (FORC) diagrams to unravel complex magnetic signals,

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Perturbation de l'echange electronique rapide par les lacunes cationiques dans Fe3−xO4(x ⩽ 0,09)

Cited by 35 publications

References 29 publications

Influence of Fe(II) on the Formation of the Spinel Iron Oxide in Alkaline Medium

Influence of Fe(II) on the Formation of the Spinel Iron Oxide in Alkaline Medium

Effect of maghemization on the magnetic properties of nonstoichiometric pseudo‐single‐domain magnetite particles

Assessing the ability of first‐order reversal curve (FORC) diagrams to unravel complex magnetic signals

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