The Effect of Low-Temperature Oxidation on Large Multi-Domain Magnetite
Decay of the virtual dipole moment during polarity transitions and geomagnetic excursions
The Effect of Low-Temperature Oxidation on Large Multi-Domain Magnetite
Decay of the virtual dipole moment during polarity transitions and geomagnetic excursions
Natural samples of oxidized and unoxidized magnetite have been used to study the effect of low-temperature oxidation on magnetic domain state. All of the magnetites studied were large multi-domain (MD) grains, ranging in size from 53 µm to at least 250 µm. Hysteresis data typical of MD grains are obtained from unoxidized magnetite samples while data from partially oxidized samples are characteristic of pseudo-single domain (PSD) grains. Our results demonstrate that low-temperature oxidation can seriously affect the magnetic properties of magnetite by significantly increasing the PSD-MD threshold size. The presence of a suppressed Verwey transition at 118 K in the oxidized samples indicates that the oxidation may only be surficial and that there may exist a core of magnetite under the maghemitized surface shell. We suggest three possible mechanisms for the observed PSD-like behavior. First, the magnetite core could be reduced sufficiently in volume to make it a PSD grain, independent of the surficial maghemite. Second, internal stress in the composite grain due to lattice mismatches between the magnetite core and maghemite rim will increase the domain wall energy and make it more difficult to add walls for a given grain size. Coupled with a reduced volume of the magnetite core, this could give rise to PSD-like behavior. Third, the composite grain could be a mixture of SD maghemite and MD magnetite which gives rise to bulk PSD-like properties. Our results have potentially important implications for paleomagnetic records because they provide a mechanism whereby a stable chemical remanent magnetization can be acquired by MD grains in sediments and igneous rocks.
757-760
Cui, Yulong
b4e2e86d-887f-4508-81ee-2a6f19c8cf2e
Verosub, Kenneth L.
396d0f22-35c1-42b9-8581-96fbb6df597d
Roberts, Andrew P.
4f062491-5408-4edb-8dd1-140c6a42e93f
1994
Cui, Yulong
b4e2e86d-887f-4508-81ee-2a6f19c8cf2e
Verosub, Kenneth L.
396d0f22-35c1-42b9-8581-96fbb6df597d
Roberts, Andrew P.
4f062491-5408-4edb-8dd1-140c6a42e93f
Cui, Yulong, Verosub, Kenneth L. and Roberts, Andrew P.
(1994)
The Effect of Low-Temperature Oxidation on Large Multi-Domain Magnetite
Decay of the virtual dipole moment during polarity transitions and geomagnetic excursions.
Geophysical Research Letters, 21 (9), .
Abstract
Natural samples of oxidized and unoxidized magnetite have been used to study the effect of low-temperature oxidation on magnetic domain state. All of the magnetites studied were large multi-domain (MD) grains, ranging in size from 53 µm to at least 250 µm. Hysteresis data typical of MD grains are obtained from unoxidized magnetite samples while data from partially oxidized samples are characteristic of pseudo-single domain (PSD) grains. Our results demonstrate that low-temperature oxidation can seriously affect the magnetic properties of magnetite by significantly increasing the PSD-MD threshold size. The presence of a suppressed Verwey transition at 118 K in the oxidized samples indicates that the oxidation may only be surficial and that there may exist a core of magnetite under the maghemitized surface shell. We suggest three possible mechanisms for the observed PSD-like behavior. First, the magnetite core could be reduced sufficiently in volume to make it a PSD grain, independent of the surficial maghemite. Second, internal stress in the composite grain due to lattice mismatches between the magnetite core and maghemite rim will increase the domain wall energy and make it more difficult to add walls for a given grain size. Coupled with a reduced volume of the magnetite core, this could give rise to PSD-like behavior. Third, the composite grain could be a mixture of SD maghemite and MD magnetite which gives rise to bulk PSD-like properties. Our results have potentially important implications for paleomagnetic records because they provide a mechanism whereby a stable chemical remanent magnetization can be acquired by MD grains in sediments and igneous rocks.
This record has no associated files available for download.
More information
Published date: 1994
Organisations:
Ocean and Earth Science
Identifiers
Local EPrints ID: 66147
URI: http://eprints.soton.ac.uk/id/eprint/66147
ISSN: 0094-8276
PURE UUID: 3039dabe-937b-44eb-a8cc-1fe8431daa9d
Catalogue record
Date deposited: 05 May 2009
Last modified: 10 Dec 2021 16:06
Export record
Contributors
Author:
Yulong Cui
Author:
Kenneth L. Verosub
Author:
Andrew P. Roberts
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics