HR: 0800h
AN: GP21B-0504    [Abstracts]
TI: New Low-Temperature Magnetic Data Acquired on Synthetic Lepidocrocite
AU: * Guyodo, Y
EM: guyodo@lsce.cnrs-gif.fr
AF: LSCE (IPSL) Laboratoire CEA-CNRS-UVSQ, Campus du CNRS, 12 Avenue de la Terrasse, Gif-sur-Yvette Cedex, 91198, France
AU: Bonville, P
EM: pierre.bonville@cea.fr
AF: SPEC CEA, DSM/DRECAM/SPEC, Gif-sur-Yvette, 91191, France
AU: Ona-Nguema, G
EM: georges.ona-nguema@impmc.jussieu.fr
AF: IMPMC, Campus Boucicaut, 140 rue de Lourmel, Paris, 75015, France
AU: Carvallo, C
EM: claire.carvallo@impmc.jussieu.fr
AF: IMPMC, Campus Boucicaut, 140 rue de Lourmel, Paris, 75015, France
AU: Wang, Y
EM: yuheng@impmc.jussieu.fr
AF: IMPMC, Campus Boucicaut, 140 rue de Lourmel, Paris, 75015, France
AU: Morin, G
EM: guillaume.morin@impmc.jussieu.fr
AF: IMPMC, Campus Boucicaut, 140 rue de Lourmel, Paris, 75015, France
AB: Lepidocrocite (γ-FeOOH) is an iron oxyhydroxide commonly found in the environment, which is assumed to be antiferromagnetic with a small ferromagnetic-like behavior and a Néel temperature of about 50K (e.g., Hirt et al., 2002, JGR, 107, 10.1029/2001JB000242). It is currently used as starting material in bio- reduction experiments leading to the formation of Fe(II)-bearing minerals such as green rusts, magnetite, and siderite (e.g., Ona-Nguema et al., 2002, Environ. Sci. Technol., 36, 16-20). Both initial and resulting materials are being characterized using various techniques including low-temperature magnetic methods.
At this meeting, results obtained on the initial synthetic lepidocrocite samples will be presented, which describe an unusual magnetic behavior. In particular, field cooled and zero field cooled induced magnetization curves (obtained using a 5mT magnetic induction) merge at a temperature around 150K (well above 50K). Below this temperature, the difference between the two curves can be qualified as a remanent magnetization, acquired during cooling of the sample in the presence of a magnetic field. As a consequence, some ferromagnetic-like behavior persists at temperatures above the admitted Néel temperature. The cooling/warming cycle of the room temperature remanent magnetization (acquired using a 2.5T magnetic induction) also indicates that some remanence can be acquired well above that temperature. Other types of measurement have been performed in order to better constrain the low-temperature magnetic behavior of these samples, in particular using a high-field VSM.
DE: 1505 Biogenic magnetic minerals
DE: 1512 Environmental magnetism
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting