Open AccessFrom Nano to Micro: Evolution of Magnetic Domain Structures in Multidomain Magnetite
Author(s) -
Nagy Lesleis,
Williams Wyn,
Tauxe Lisa,
Muxworthy Adrian R.
Publication year - 2019
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2019gc008319
Subject(s) - magnetite , single domain , micromagnetics , remanence , domain (mathematical analysis) , magnetic domain , condensed matter physics , geology , grain size , domain wall (magnetism) , vortex state , demagnetizing field , magnetic field , materials science , physics , magnetization , mathematics , geomorphology , paleontology , mathematical analysis , superconductivity , quantum mechanics
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 ( ≿ 10 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.