Open AccessHysteresis of Natural Magnetite Ensembles: Micromagnetics of Silicate‐Hosted Magnetite Inclusions Based on Focused‐Ion‐Beam Nanotomography
Author(s) -
Nikolaisen Even S.,
Harrison Richard J.,
Fabian Karl,
McEnroe Suzanne A.
Publication year - 2020
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2020gc009389
Subject(s) - magnetite , pyroxene , plagioclase , mineralogy , geology , hysteresis , anisotropy , single domain , materials science , grain size , remanence , magnetic hysteresis , silicate , condensed matter physics , analytical chemistry (journal) , magnetization , magnetic domain , olivine , physics , magnetic field , quartz , chemistry , optics , composite material , metallurgy , geomorphology , quantum mechanics , astronomy , chromatography
Abstract Three‐dimensional geometries of silicate‐hosted magnetic inclusions from the Harcus intrusion, South Australia have been determined using focused‐ion‐beam nanotomography (FIB‐nt). By developing an effective workflow, the geometries were reconstructed for magnetic particles in a plagioclase (162) and a pyroxene (282), respectively. For each inclusion, micromagnetic modeling using Micromagnetic Earth Related Rapid Interpreted Language Laboratory provided averaged hysteresis loops and backfield remanence curves of 20 equidistributed field directions together with average M s , M rs , H c , and H cr . The micromagnetic structures within each silicate are single‐domain (SD), single‐vortex (SV), multivortex (MV) and multidomain states. They have been analyzed using domain‐state diagnostic plots, such as the Day plot and the Néel plot. SD particles can be subdivided into groups with dominant uniaxial anisotropy ( M rs / M s ∼0.5 and 10 < H c < 100 mT) and mixed uniaxial/multiaxial anisotropy ( M rs / M s ∼0.7 and 10 < H c < 30 mT). Most SV particles lie on a trend with 0 < M rs / M s < 0.1 and 0 < H c < 10 mT, while others display a broad range of intermediate M rs / M s and H c values. SV and MV states do not plot on systematic grain‐size trends. Instead, the multicomponent mixture of domain states within each silicate spans the entire range of natural variability seen in bulk samples. This questions the interpretation of bulk average hysteresis parameters in terms of grain size alone. FIB‐nt combined with large‐scale micromagnetic simulations provides a more complete characterization of silicate‐hosted carriers of stable magnetic remanence. This approach will improve the understanding of single‐crystal paleomagnetism and enable primary paleomagnetic data to be extracted from ancient rocks.