The Vortex State in Geologic Materials: A Micromagnetic Perspective

Lascu, Ioan and Einsle, Joshua F. and Ball, Matthew R. and Harrison, Richard J. (2018) The Vortex State in Geologic Materials: A Micromagnetic Perspective. Journal of Geophysical Research: Solid Earth, 123 (9). pp. 7285-7304. ISSN 21699313 DOI https://doi.org/10.1029/2018JB015909

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Abstract

A wide variety of Earth and planetary materials are very good recorders of paleomagnetic information. However, most magnetic grains in these materials are not in the stable single domain grain size range but are larger and in nonuniform vortex magnetization states. We provide a detailed account of vortex phenomena in geologic materials by simulating first‐order reversal curves (FORCs) via finite‐element micromagnetic modeling of magnetite nanoparticles with realistic morphologies. The particles have been reconstructed from focused ion beam nanotomography of magnetite‐bearing obsidian and accommodate single and multiple vortex structures. Single vortex (SV) grains have fingerprints with contributions to both the transient and transient‐free zones of FORC diagrams. A fundamental feature of the SV fingerprint is a central ridge, representing a distribution of negative saturation vortex annihilation fields. SV irreversible events at multiple field values along different FORC branches determine the asymmetry in the upper and lower lobes of generic bulk FORC diagrams of natural materials with grains predominantly in the vortex state. Multivortex (MV) FORC signatures are modeled here for the first time. MV grains contribute mostly to the transient‐free zone of a FORC diagram, averaging out to create a broad central peak. The intensity of the central peak is higher than that of the lobes, implying that MV particles are more abundant than SV particles in geologic materials with vortex state fingerprints. The abundance of MV particles, as well as their single domain‐like properties point to MV grains being the main natural remanent magnetization carriers in geologic materials.

Item Type:	Article
Uncontrolled Keywords:	2018AREP, IA74
Subjects:	03 - Mineral Sciences
Divisions:	03 - Mineral Sciences 06 - Part-III Projects 08 - Green Open Access 12 - PhD
Journal or Publication Title:	Journal of Geophysical Research: Solid Earth
Volume:	123
Page Range:	pp. 7285-7304
Identification Number:	https://doi.org/10.1029/2018JB015909
Depositing User:	Sarah Humbert
Date Deposited:	08 Feb 2019 13:47
Last Modified:	12 Sep 2019 09:41
URI:	http://eprints.esc.cam.ac.uk/id/eprint/4421

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