Chemical remanent magnetization of the FeOOH, Fe2O3 system

Hedley, Ian

doi:10.1016/0031-9201(68)90055-1

Cited by 65 publications

(45 citation statements)

References 21 publications

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“…The conversion to ferrimagnetic maghemite is complete at approximately 300~ as indicated by the maximum in bulk susceptibility and in magnetization (Figure 1 and 2). These results are in good agreement with calorimetric data that showed an endothermic enthalpy change during the transformation of lepidocrocite to maghemite at similar temperatures (Hedley, 1968;G6-mez-Villacieros et al, 1984). The decay of magnetization above 300~ can be explained by the generation of hematite that carries a weak antiferromagnetism.…”

Section: Discussionsupporting

confidence: 90%

The Transformation of Lepidocrocite During Heating: A Magnetic and Spectroscopic Study

Gehring

Hofmeister

1994

Clays and clay miner.

117

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Abstract--Infrared (IR) spectroscopy, in combination with magnetic methods, was used to study the thermally induced transformation of synthetic lepidocrocite (3,-FeOOH) to maghemite (~-Fe203). Magnetic analyses showed that the thermal conversion began at about 175"C with the formation of superparamagnetic maghemite clusters. The overall structural transformation to ferrimagnetic'y-Fe203 occurred at 200"C and was complete around 300"C. At higher temperatures, the maghemite converted into hematite (a-Fe203). Observation of the transformation from 3,-FeOOH to "y-Fe203 using variable-temperature IR spectroscopy indicated that dehydroxilation on a molecular level was initiated between 145"C and 155*C. The lag time between the onset of the breaking of OH bonds and the release of H20 from lepidocrocite around 1750C can be explained by diffusive processes. Overall dehydroxilation and the subsequent breakdown of the lepidocrocite structure was complete below 219*(3. The comparison of the magnetic and IR data provides evidence that the dehydroxilation may precede the structural conversion to maghemite.

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Section: Discussionsupporting

confidence: 90%

The Transformation of Lepidocrocite During Heating: A Magnetic and Spectroscopic Study

Gehring

Hofmeister

1994

Clays and clay miner.

117

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“…Hedley [12] has reported similar results for fine particles of hematite. The author has attributed the depression of T (M) to its known sensitivity to pressure in this system.…”

Section: ____________________________________________________________supporting

confidence: 67%

Properties of magnetite nanoparticles synthesized through a novel chemical route

et al. 2004

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We have developed a simple precipitation route to synthesize magnetite (Fe 3 O 4 ) nanoparticles with controlled size without any requirement of calcination step at high temperatures. The study of these nano-particles indicates an enhancement in saturation magnetization with reduction in size down to ~10 nm beyond which the magnetization reduces. The latter is attributed to surface effects becoming predominant as surface to core volume ratio increases. From the view -point of applications, 10 nm size of magnetite particles seems to be the optimum.

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“…To further our understanding of CRM in red beds, the acquisition process of CRM in hematite has been simulated experimentally in the laboratory (Hedley, 1968;Bailey and Hale, 1981;Stokking and Tauxe, 1987,1990a, 1990bÖzdemir and Dunlop, 1993;Gendler et al, 2005). Two types of CRM are distinguished growth-CRM and alteration-CRM: the first involves growing of the magnetic minerals through the SP threshold; the second implies the alteration of an existing magnetic mineral to another magnetic mineral at a temperature below the magnetic ordering temperature.…”

Section: Introductionmentioning

confidence: 99%

Acquisition of chemical remanent magnetization during experimental ferrihydrite–hematite conversion in Earth-like magnetic field—implications for paleomagnetic studies of red beds

Jiang

Liu

Dekkers

et al. 2015

Earth and Planetary Science Letters

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Hematite-bearing red beds are renowned for their chemical remanent magnetization (CRM). If the CRM was acquired substantially later than the sediment was formed, this severely compromises paleomagnetic records. To improve our interpretation of the natural remanent magnetization, the intricacies of the CRM acquisition process must be understood. Here, we contribute to this issue by synthesizing hematite under controlled 'Earth-like' field conditions (< ~100 µT).CRM was imparted in 90 oriented samples with varying inclinations. The final magnetic remanence carrier is hematite with traces of ferrimagnetic ferrihydrite or maghemite. When the magnetic field intensity is > ~40 µT, CRM of hematite records the field direction faithfully. However, for growth field intensities < ~40 µT, the CRM direction may deviate considerably from that of the growth field. The CRM intensity normalized by the isothermal remanent magnetization (CRM/IRM @2.5 T ) increases linearly with the intensity of growth field, implying that CRM could potentially be useful for relative paleointensity studies. The hematite CRM has a distributed unblocking temperature spectrum from ~200 to ~650 °C while hematite with a depositional remanent magnetization (DRM) has a more confined spectrum from ~600 to 680 °C. Further, the CRM thermal demagnetization curves with their concave shape are notably different from their DRM counterparts which are convex. These differences together are suggested to be a potential discriminator of CRM from DRM carried by hematite in natural red beds, and of significance for the interpretation of paleomagnetic studies on red beds.

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Chemical remanent magnetization of the FeOOH, Fe2O3 system

Cited by 65 publications

References 21 publications

The Transformation of Lepidocrocite During Heating: A Magnetic and Spectroscopic Study

The Transformation of Lepidocrocite During Heating: A Magnetic and Spectroscopic Study

Properties of magnetite nanoparticles synthesized through a novel chemical route

Acquisition of chemical remanent magnetization during experimental ferrihydrite–hematite conversion in Earth-like magnetic field—implications for paleomagnetic studies of red beds

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