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Widespread occurrence of a novel high coercivity, thermally stable, low unblocking temperature magnetic phase in heated archeological material
Author(s) -
McIntosh G.,
Kovacheva M.,
Catanzariti G.,
Osete M. L.,
Casas L.
Publication year - 2007
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2007gl031168
Subject(s) - coercivity , remanence , materials science , phase (matter) , hematite , thermal stability , thermal decomposition , cristobalite , mineralogy , goethite , nuclear magnetic resonance , analytical chemistry (journal) , geology , chemical engineering , composite material , magnetization , condensed matter physics , chemistry , metallurgy , magnetic field , physics , quartz , organic chemistry , quantum mechanics , chromatography , engineering , adsorption
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 distinguishing 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 ɛ‐Fe 2 O 3 .