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From nano to micro: evolution of magnetic domain structures in multi‐domain magnetite

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Title: From nano to micro: evolution of magnetic domain structures in multi‐domain magnetite
Authors: Nagy, L
Williams, W
Tauxe, L
Muxworthy, AR
Item Type: Journal Article
Abstract: Reliability of magnetic recordings of the ancient magnetic field is strongly dependent on the magnetic mineralogy of natural samples. Theoretical estimates of long‐term stability of remanence were restricted to single‐domain (SD) states, but micromagnetic models have recently demonstrated that the so‐called single‐vortex (SV) domain structure can have even higher stability that SD grains. In larger grains ( urn:x-wiley:ggge:media:ggge21913:ggge21913-math-000110 μm in magnetite) the multidomain (MD) state dominates, so that large uniform magnetic domains are separated by narrow domain walls. In this paper we use a parallelized micromagnetic finite element model to provide resolutions of many millions of elements allowing us, for the first time, to examine the evolution of magnetic structure from a uniform state, through the SV state up to the development of the domain walls indicative of MD states. For a cuboctahedral grain of magnetite, we identify clear domain walls in grains as small as ∼3 μm with domain wall widths equal to that expected in large MD grains; we therefore put the SV to MD transition at ∼3 μm for magnetite and expect well‐defined, and stable, SV structures to be present until at least ∼1 μm when reducing the grain size. Reducing the size further shows critical dependence on the history of domain structures, particularly with SV states that transition through a so‐called “unstable zone” leading to the recently observed hard‐aligned SV states that proceed to unwind to SD yet remain hard aligned.
Issue Date: Jun-2019
Date of Acceptance: 15-May-2019
URI: http://hdl.handle.net/10044/1/70884
DOI: 10.1029/2019gc008319
ISSN: 1525-2027
Publisher: American Geophysical Union
Start Page: 2907
End Page: 2918
Journal / Book Title: Geochemistry, Geophysics, Geosystems
Volume: 20
Issue: 6
Copyright Statement: ©2019. American Geophysical Union.All Rights Reserved.
Sponsor/Funder: Natural Environment Research Council (NERC)
Natural Environment Research Council (NERC)
Funder's Grant Number: NE/J020508/1
NE/S001018/1
Keywords: Science & Technology
Physical Sciences
Geochemistry & Geophysics
single vortex
multidomain
domain state evolution
magnetite
Bloch wall
3-DIMENSIONAL MICROMAGNETIC CALCULATIONS
PARTICLES
04 Earth Sciences
02 Physical Sciences
Geochemistry & Geophysics
Publication Status: Published
Open Access location: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GC008319
Online Publication Date: 2019-06-22
Appears in Collections:Faculty of Engineering
Earth Science and Engineering



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