Grain size dependence of low-temperature remanent magnetization in natural and synthetic magnetite: Experimental study
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Published:2009-01
Issue:1
Volume:61
Page:119-124
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ISSN:1343-8832
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Container-title:Earth, Planets and Space
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language:en
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Short-container-title:Earth Planet Sp
Author:
Smirnov Aleksey V.
Abstract
Abstract
Magnetic measurements at cryogenic temperatures (<300 K) proved to be useful in paleomagnetic and rock magnetic research, stimulating continuous interest to low-temperature properties of magnetite and other magnetic minerals. Here I report new experimental results on a grain size dependence of the ratio (R
LT) between a low-temperature (20 K) saturation isothermal remanent magnetization (SIRM) imparted in magnetite after cooling in a 2.5 T field (field cooling, FC) and in a zero field environment (zero field cooling, ZFC). Synthetic magnetite samples ranged in mean grain size from 0.15 to 100 μm, representing nearly single-domain (SD), pseudosingle-domain (PSD), and multidomain (MD) magnetic states. The R
LT ratio monotonically increases from 0.58 to 1.12 with the decreasing mean grain size, being close to unity for PSD grains (0.15-5 μm) and smaller than unity for MD magnetite (12-100 μm). The R
LT ratio of 1.27 is observed for acicular magnetite characterized by nearly SD behavior. These observations indicate that within the range of ~0.15 to ~5 μm, the low-temperature SIRM may be higher than that expected from “normal” magnetic domain wall displacement. Such a behavior can be caused by the presence of a SD-like component in the magnetization of these grains, which origin, however, is uncertain. The natural rocks containing nearly stoichiometric magnetite manifest a dependence of the R
LT ratio on magnetic domain state identical to that observed from synthetic magnetites. Therefore, the comparison of FC SIRM and ZFC SIRM at very low temperatures may allow a crude estimate of magnetic domain state in some magnetite-bearing rocks, such as shallow mafic intrusions or some marine sediments.
Publisher
Springer Science and Business Media LLC
Subject
Space and Planetary Science,Geology
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