Open AccessEpsilon iron oxide: Origin of the high coercivity stable low C urie temperature magnetic phase found in heated archeological materials
Author(s) -
LópezSánchez J.,
McIntosh G.,
Osete M. L.,
del Campo A.,
Villalaín J. J.,
Pérez L.,
Kovacheva M.,
Rodríguez de la Fuente O.
Publication year - 2017
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2017gc006929
Subject(s) - maghemite , coercivity , curie temperature , remanence , raman spectroscopy , hematite , geology , rutile , mineralogy , iron oxide , materials science , oxide , magnetite , analytical chemistry (journal) , phase (matter) , ilmenite , nuclear magnetic resonance , magnetization , chemistry , metallurgy , ferromagnetism , condensed matter physics , magnetic field , physics , organic chemistry , paleontology , quantum mechanics , chromatography , optics
The identification of epsilon iron oxide (ɛ‐Fe 2 O 3 ) as the low Curie temperature high coercivity stable phase (HCSLT) carrying the remanence in heated archeological samples has been achieved in samples from two archeological sites that exhibited the clearest evidence of the presence of the HCSLT. This uncommon iron oxide has been detected by Confocal Raman Spectroscopy (CRS) and characterized by rock magnetic measurements. Large numbers of ɛ‐Fe 2 O 3 microaggregates (in CO) or isolated clusters (in HEL) could be recognized, distributed over the whole sample, and embedded within the ceramic matrix, along with hematite and pseudobrookite and with minor amounts of anatase, rutile, and maghemite. Curie temperature estimates of around 170°C for CO and 190°C for HEL are lower than for pure, synthetic ɛ‐Fe 2 O 3 (227°C). This, together with structural differences between the Raman spectra of the archeologically derived and synthetic samples, is likely due to Ti substitution in the ɛ‐Fe 2 O 3 crystal lattice. The γ‐Fe 2 O 3 ‐ɛ‐Fe 2 O 3 ‐α‐Fe 2 O 3 transformation series has been recognized in heated archeological samples, which may have implications in terms of their thermal history and in the factors that govern the formation of ɛ‐Fe 2 O 3 .