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HIGH CRYSTALLINITY SI-FERRIHYDRITE: AN INSIGHT INTO ITS NÉEL TEMPERATURE AND SIZE DEPENDENCE OF MAGNETIC PROPERTIES
Citation:
BERQUO', T. S., S. K. BANERJEE, R. FORD, R. L. PENN, AND T. PICHLER. HIGH CRYSTALLINITY SI-FERRIHYDRITE: AN INSIGHT INTO ITS NÉEL TEMPERATURE AND SIZE DEPENDENCE OF MAGNETIC PROPERTIES. D. McKnight (ed.), JOURNAL OF GEOPHYSICAL RESEARCH. American Geophysical Union, Washington, DC, 112(B02102, doi:10.):1-12, (2007).
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Description:
Ferrihydrite, an antiferromagnetic iron oxyhydroxide, is of great importance for the cycling of many trace metals in the environment. Four ferrihydrite samples prepared with 1.3 to 3.5 wt% of Si at different synthesis temperatures (7.5 °C, 22 °C, 50 °C and 75 °C) were studied by temperature dependent hysteresis loops, ZFC/FC susceptibility curves, ac susceptibility and Mössbauer spectroscopy. The incorporation of Si into the ferrihydrite during synthesis changed the properties of this mineral. Interesting, seven sharp lines were observed in the X-ray diffraction pattern of the ferrihydrite samples prepared at 50 °C and 75 °C. In general, both XRD and magnetism demonstrate that particle size decreased (from 23 nm to 2 nm) and particle size distribution narrowed as the synthesis temperature was lowered. Those samples prepared between 7.5 °C and 50 °C showed the expected superparamagnetic behavior of ferrihydrite below 300 K. The ferrihydrite prepared at 75 °C was unusually coarse-grained and had a blocking temperature above 300 K. Extrapolation of induced magnetization from the largest particles with the highest crystallinity allowed an estimate of a ferrihydrite Néel temperature of around 422 K. We also present XRD and magnetic data from large natural Si-ferrihydrite collected from a marine shallow-water hydrothermal area that formed at a temperature of approximately 88 °C.
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HIGH CRYSTALLINITY SI-FERRIHYDRITE: AN INSIGHT INTO ITS NÉEL TEMPERATURE AND SIZE DEPENDENCE OF MAGNETIC PROPERTIES