HR: 09:00h
AN: GP21C-05    [Abstracts]
TI: Low Temperature Demagnetization of Chemical Remanent Magnetization in Magnetite
AU: * Ozdemir, O
EM: ozdemir@physics.utoronto.ca
AF: University of Toronto, Chemical and Physical Sciences, 3359 Mississauga Road North, Mississauga, ON L5L 1C6 Canada
AB: Chemical remanent magnetization (CRM) has been studied for partially oxidized submicron synthetic (270 nm) and natural (500 nm) magnetites, before and after low-temperature demagnetization (LTD), which consists of zero field cycling through the Verwey transition. CRM's were produced at constant temperatures of 100, 150 and 200 C in controlled field. The intensity of CRM increased as the temperature of the run increased for both samples. AF demagnetization curves were soft before LTD, but became harder after LTD. The CRM memories have a much more SD-like shape to their AF decay curves than the original untreated remanences. Initial plateaus are well developed. The memory fraction of CRM's for the partially oxidized samples increased from 0.39 to 0.77 as the temperature of the run increased from 100 to 200 C. The increases reflect the fact that the remanences carried by SD moments are pinned by magnetoelastic anisotropy rather than crystalline anisotropy and thus survive LTD. This is because magnetic memory is controlled in part by the internal stresses developed at the magnetite-maghemite interface during oxidation. Low-temperature saturation remanent magnetization (SIRM) has also been measured for the partially oxidized magnetites. With increasing low-temperature oxidation, the Verwey transition becomes blurred, shifts to lower temperatures and eventually disappears. The SIRM memories for the partially oxidized samples increased with increasing oxidation to maghemite. LTD might provide a method of separating remanence of chemical origin from primary remanence.
DE: 1517 Magnetic anomaly modeling
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
DE: 1533 Remagnetization
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting