Saturation magnetisation, coercivity and lattice parameter changes in the system Fe3O4-?Fe2O3, and their relationship to structure

Goss, C. J.

doi:10.1007/bf00203200

Cited by 87 publications

(48 citation statements)

References 25 publications

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“…However, a slight oxidative process appears at approximately 250 °C, which increases with increasing temperature according to the higher amount of maghemite observed in system II. Similar results were recorded in another study, showing that conversion from magnetite to maghemite can be accomplished at approximately 220 °C; this process is considered as a single phase topotactic reaction in which the oxide ion lattice remains cubic‐packed and the oxygen layers are added as the iron cations migrate to the surface …”

Section: Resultssupporting

confidence: 86%

Influence of two structural phases of Fe₃O₄and γ-Fe₂O₃on the properties of polyimide/iron oxide composites

Nica¹,

Nica

Grigoraş³

et al. 2015

Polym. Int.

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Partially aliphatic polyimide/iron oxide composites based on the poly(amic acid) from 5-(2,5-dioxotetrahydro-3-furyl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride and 4,4 ′ -oxydianiline with iron oxide in different weight percentages were obtained. The structural phases of the transition of magnetite to maghemite occurring in these composites, at different temperatures, are discussed. The physical characteristics, including magnetic, thermal, structural and morphological properties, evaluated using X-ray diffraction, scanning electron microscopy and thermal analysis, are influenced by the interplay of the filler content and the structural changes of the composite. The X-ray diffraction patterns of all samples show a cubic structure indexed as magnetite (Fe 3 O 4 ) or maghemite ( -Fe 2 O 3 ). Quantification of these two phases was evidenced by the Rietveld method. The electrical properties analysed under different humidity conditions evidence the potential applicability of these polyimide/iron oxide materials as humidity sensors.

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Section: Resultssupporting

confidence: 86%

Influence of two structural phases of Fe₃O₄and γ-Fe₂O₃on the properties of polyimide/iron oxide composites

Nica¹,

Nica

Grigoraş³

et al. 2015

Polym. Int.

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“…The existence of at least two metastable maghemites, a low‐ and a high‐temperature form, during the course of oxidation of magnetite to haematite was proposed by Goss (1988). The first maghemite has a face‐centred cubic lattice, the second a primitive cubic structure.…”

Section: Discussionmentioning

confidence: 99%

The lepidocrocite-maghemite-haematite reaction chain-I. Acquisition of chemical remanent magnetization by maghemite, its magnetic properties and thermal stability

Gendler

Щербаков²,

Dekkers³

et al. 2005

Geophysical Journal International

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SUMMARY We report on the magnetic properties and the acquisition of a chemical remanent magnetization (CRM) in a field of 100 μT as a function of temperature and time during the lepidocrocite–maghemite–haematite reaction chain. The development of CRM was monitored at a series of 13 temperatures ranging from 175 to 550 °C; data acquisition was done at the specific formation temperatures for durations of up to 500 hr. Up to acquisition temperatures of 200 °C it takes a considerable time (up to 7 hr) before the CRM is measurable. This time decreases with increasing temperature, reflecting the activation energy of the reaction to form the first maghemite. During the lepidocrocite conversion, formation of two types of maghemite is suggested by two peaks in the CRM versus time curves. Magnetic properties were analysed after various stages in the reaction. They indicate a mixture of superparamagnetic and single‐domain maghemite. The first reaction product (obtained after annealing at 200 °C) is a fine‐grained yet crystalline maghemite (labelled type A). Before massive maghemite formation occurs, the coercive and remanent coercive forces go through a minimum at intermediate temperatures of 250–300 °C (annealing for 2.5 hr). This minimum lowers to 200–250 °C with increasing annealing time (500 hr). This is probably the result of two processes acting simultaneously—formation of superparamagnetic maghemite particles of a second less crystalline maghemite type (labelled type B) and removal of stacking faults in type A maghemite. The second process is suggested by analogy to the behaviour of natural magnetite/maghemite systems on annealing. Removal of stacking faults is reported to result in a magnetic softening of the grain assemblage. Annealing at 300–350 °C removes most of the lepidocrocite and the second maghemite type, type B, becomes prominent. Haematite formation sets in at slightly higher temperatures, yet the type B maghemite is in part thermally stable up to 600 °C enabling Thellier–Thellier experiments. This stability is also inferred from Arrhenius fitting that shows a comparatively high activation energy for the maghemite to haematite reaction. In Thellier–Thellier experiments the CRM showed a markedly downward convex Arai–Nagata plot while a second thermoremanent magnetization (TRM) showed perfect linear behaviour as expected. This feature may be used to recognize CRM in natural rocks.

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“…Reduced values of Js are often reported for natural maghemites and are here possibly caused by the substitution of diamagnetic At [cf. Goss, 1988]. The remanence ratios (Jrs/Js) and coercivity ratios (Hcr/Hc) range 0.12-0.16 and 2.54-2.67, respectively (Table 1).…”

Section: Rock Magnetic Parameters At Room Temperaturementioning

confidence: 98%

Grain‐size dependence of the rock magnetic properties for a natural maghemite

Boer¹,

Dekkers²

1996

Geophysical Research Letters

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The natural maghemite from the Robe River mining district (Australia) is shown to be thermally very stable. The maghemite/hematite inversion occurs at -650øC for sized fractions (250 gm to < 5 gm), enabling determination of T c for maghemite at 610øC. The maghemite is intimately intergrown with hematite and Js of the maghemite (corrected for the hematite content) is 64 Am2/kg ß Jrs, Hcr and H c range between 7.46 -10.18 Am2/kg, 16.90 -23.30 mT, and 6.38 -9.00 mT respectively, indicating PSD maghemite with grain sizes between -1 and -20 gm. The grain-size dependence of the rock magnetic parameters of the maghemite is less prominent than those of magnetite of nominally the same size. It is suggested that the LT-behavior of ARM can be diagnostic of the presence of maghemite: upon cooling to -196øC it shows no change; upon rewarming a gradual decrease in intensity occurs starting at --120øC.

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Saturation magnetisation, coercivity and lattice parameter changes in the system Fe3O4-?Fe2O3, and their relationship to structure

Cited by 87 publications

References 25 publications

Influence of two structural phases of Fe₃O₄and γ-Fe₂O₃on the properties of polyimide/iron oxide composites

Influence of two structural phases of Fe₃O₄and γ-Fe₂O₃on the properties of polyimide/iron oxide composites

The lepidocrocite-maghemite-haematite reaction chain-I. Acquisition of chemical remanent magnetization by maghemite, its magnetic properties and thermal stability

Grain‐size dependence of the rock magnetic properties for a natural maghemite

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Saturation magnetisation, coercivity and lattice parameter changes in the system Fe3O4-?Fe2O3, and their relationship to structure

Cited by 87 publications

References 25 publications

Influence of two structural phases of Fe3O4and γ-Fe2O3on the properties of polyimide/iron oxide composites

Influence of two structural phases of Fe3O4and γ-Fe2O3on the properties of polyimide/iron oxide composites

The lepidocrocite-maghemite-haematite reaction chain-I. Acquisition of chemical remanent magnetization by maghemite, its magnetic properties and thermal stability

Grain‐size dependence of the rock magnetic properties for a natural maghemite

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Influence of two structural phases of Fe₃O₄and γ-Fe₂O₃on the properties of polyimide/iron oxide composites

Influence of two structural phases of Fe₃O₄and γ-Fe₂O₃on the properties of polyimide/iron oxide composites