Widespread occurrence of a novel high coercivity, thermally stable, low unblocking temperature magnetic phase in heated archeological material

G. McIntosh, M. Kovacheva, G. Catanzariti, M. L. Osete, L. Casas

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Abstract

The widespread occurrence of a novel, high coercivity magnetic phase in well-heated archeological material is reported. Its properties are defined when it represents the dominant magnetic phase, although it is nearly always found as part of a mixture of magnetic phases. They are as follows: very high coercivity (remanence coercivity >600 mT), low unblocking temperatures (≤200°C) and high degree of thermal stability-this last property istinguishing it from goethite. The phase shows striking similarities to magnetic phases produced by thermal decomposition of nontronite (an Fe-rich clay), where decomposition occurs after prolonged heating in air to high temperatures - conditions suffered by well-heated archeomagnetic material. Preliminary results of Mössbauer and X-Ray diffraction spectroscopy suggest that the phase is more likely to be a substituted hematite, rather than Fe-cristobalite or a variant of ε-Fe2O3. Copyright 2007 by the American Geophysical Union.
Original languageEnglish
Article numberL21302
JournalGeophysical Research Letters
Volume34
DOIs
Publication statusPublished - 16 Nov 2007

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