HR: 17:00h
AN: GP24A-05    [Abstracts]
TI: Fundamental Magnetic Properties from Pure Synthetic Greigite
AU: * Chang, L
EM: chang1@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southamton, Waterfront Campus, European Way, Southampton, SO14 3ZH, United Kingdom
AU: Roberts, A P
EM: arob@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southamton, Waterfront Campus, European Way, Southampton, SO14 3ZH, United Kingdom
AU: Muxworthy, A R
EM: adrian.muxworthy@imperial.ac.uk
AF: Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, United Kingdom
AU: Tang, Y
EM: ty1977@mail.ustc.edu.cn
AF: Hefei National Laboratory for Physical Sciences at Microscale and Department of Materials Science and Engineering, University of Science and Technology of China, Hefei, 230026, China
AU: Chen, Q
EM: cqw@ustc.edu.cn
AF: Hefei National Laboratory for Physical Sciences at Microscale and Department of Materials Science and Engineering, University of Science and Technology of China, Hefei, 230026, China
AU: Rainford, B D
EM: bdr@phys.soton.ac.uk
AF: School of Physics and Astronomy, University of Southampton, Highfield Campus, Southampton, SO17 1BJ, United Kingdom
AB: Greigite (Fe₃S₄), an authigenic mineral that forms in sulfate-reducing environments, has been widely identified in marine and lake sediments. It is often the main magnetic carrier in some settings, and can therefore be significant in paleomagnetic and environmental magnetic studies. However, unlike its iron oxide counterpart, magnetite (Fe₃O₄), the fundamental magnetic characteristics of greigite are still poorly understood, which is partially due to the metastability of greigite and the difficulty in obtaining high quality greigite samples. We have successfully synthesized pure greigite samples with good crystallinity using a new hydrothermal method. Our detailed low- and high-temperature magnetic measurements document the previously poorly known magnetic properties of greigite, including the first accurate measurement of its saturation magnetization. We have for the first time unambiguously determined the magnetic structure of greigite by combined neutron powder diffraction and neutron polarization analysis. Low temperature (LT) neutron diffraction spectra reveal the temperature dependence of sublattice magnetizations. The pure synthetic greigite samples are large enough to show pseudo-single-domain (PSD) and multi-domain (MD) behavior. LT cycling (LTC) of saturation isothermal remanent magnetization (SIRM) measurements indicate a continuous demagnetization of remanence during cooling. Preservation of the main features of first-order reversal curve distributions at LT, coupled with LT SIRM warming curves, rule out the presence of substantial superparamagnetic behavior in the studied samples. No LT magnetic transition has been detected; however, a local coercivity minimum is observed at around 130 K. These fundamental studies provide new constraints on the magnetic behaviour of greigite.
DE: 1512 Environmental magnetism
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1540 Rock and mineral magnetism
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting