HR: 0800h
AN: GP41A-0861 [Abstracts]
TI: Non Saturation of the Defect Moment of Goethite and Fine-Grained Hematite up to 60 Teslas
AU: * Math‚, P
EM: mathe@cerege.fr
AF: University of Aix Marseille 3, CEREGE BP80 Cedex 4, Aix en Provence, 13545
France
AU: Rochette, P
EM: rochette@cerege.fr
AF: University of Aix Marseille 3, CEREGE BP80 Cedex 4, Aix en Provence, 13545
France
AU: Esteban, L
EM: esteban@lmtg.obs-mip.fr
AF: University of Toulouse, LMTG, Toulouse, 31400
France
AU: Rakoto, H
EM: rakoto@insa-tlse.fr
AF: Laboratoire National des Champs Magn‚tiques Puls‚s, INSA, Toulouse, 31400
France
AU: Bouchez, J
EM: bouchez@lmtg.obs-mip.fr
AF: University of Toulouse, LMTG, Toulouse, 31400
France
AU: Liu, Q
EM: liux0272@yahoo.com
AF: UCSD, Institute of Geophysics and Planetary Physics, Santa Cruz, CA 95064
United States
AU: Torrent, J
EM: cr1tocaj@uco.es
AF: University of Cordoba, Departamento de Ciencias y Recursos Agr¡colas y Forestales, Cordoba, 14080
Spain
AB:
Defect moment of antiferromagnets yield the highest remanent coercivity observed among minerals, and previous studies have
been unable to reach saturation of isothermal remanent magnetization (IRM) in some goethite and hematite, even up to 20
Teslas, using resistive Bitter magnets. To go further the acquisition of IRM at room temperature has been monitored on
various natural and synthetic goethite and hematite samples in pulsed magnetic fields up to 57 Teslas. "Coarse" hematite is
saturated around 5-10 T, and low unblocking temperature (i.e. with low crystallinity or Al substitution) goethites around 20
T. Higher Tb goethites and a Mn bearing fine-grained hematite are still not saturated at 57 T, with only 2 to 10 percent of
the maximum IRM acquired in 3 T. Half acquisition fields are mostly above 10 T. This indicates that usual rock magnetic
techniques are practically blind to such minerals. IRM acquisition is strongly irreversible: in some samples a 57 T backfield
is unable to fully erase a previous 38 T IRM. A field induced defect diffusion model is put forward to account for
remanence acquisition in these materials.
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005