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Variations of magnetic Verwey transition: New insights through magnetic susceptibility of magnetite-rich rocks deformed under laboratory seismic-related fatigue loadings

Fuchs, Helena; Reznik, Boris; Schilling, Frank R.; Kontny, Agnes

Abstract (englisch):
At about 120 K magnetite undergoes a sharp Verwey transition (TV) caused by atom coordination changes through a monoclinic to cubic phase transition (e.g. Dunlop and Özdemir 1997). TV is sensitive to composition, oxidation and pressure and can be determined by temperature-dependent magnetic susceptibility measurements (k-T curves, see e.g. Reznik et al., 2016 and references therein). The shape across the transition is rather complex in magnetite-bearing rocks compared to single crystal experiments, consisting of at least a sigmoidal increase followed by exponential decay.

In the present work a new approximation procedure is developed which considers the complete shape of the transition region for modelling, using superposition of infinitesimally small magnetite volumes similar to magnetic domains whereby different transition temperatures for different domains are assumed. Such temperature variations may be caused e.g. by internal stresses. The procedure allows a precise fitting even in the range of peak susceptibility where both, sigmoidal increase and exponential decay, have a strong influence on the measured susceptibility, leading to a quantitative determination of shape parameters correlating with deformation conditions of the examined rocks.
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Zugehörige Institution(en) am KIT Institut für Angewandte Geowissenschaften (AGW)
Publikationstyp Vortrag
Publikationsdatum 24.09.2019
Sprache Englisch
Identifikator KITopen-ID: 1000105292
HGF-Programm 35.14.01 (POF III, LK 01) Effiziente Nutzung geothermisch. Energie
Veranstaltung GeoMünster (2019), Münster, Deutschland, 22.09.2019 – 25.09.2019
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