title: Direct visualization of the thermomagnetic behavior of pseudo-single-domain magnetite particles.
abstract: The study of the paleomagnetic signal recorded by rocks allows scientists to understand Earth's past magnetic field and the formation of the geodynamo. The magnetic recording fidelity of this signal is dependent on the magnetic domain state it adopts. The most prevalent example found in nature is the pseudo-single-domain (PSD) structure, yet its recording fidelity is poorly understood. Here, the thermoremanent behavior of PSD magnetite (Fe3O4) particles, which dominate the magnetic signatures of many rock lithologies, is investigated using electron holography. This study provides spatially resolved magnetic information from individual Fe3O4 grains as a function of temperature, which has been previously inaccessible. A small exemplar Fe3O4 grain (~150 nm) exhibits dynamic movement of its magnetic vortex structure above 400°C, recovering its original state upon cooling, whereas a larger exemplar Fe3O4 grain (~250 nm) is shown to retain its vortex state on heating to 550°C, close to the Curie temperature of 580°C. Hence, we demonstrate that Fe3O4 grains containing vortex structures are indeed reliable recorders of paleodirectional and paleointensity information, and the presence of PSD magnetic signals does not preclude the successful recovery of paleomagnetic signals.
authors.affiliation: Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors.forename: Trevor P
authors.identifier: 0000-0003-4683-6279
authors.initials: TP
authors.lastname: Almeida
authors.affiliation: Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
authors.forename: Adrian R
authors.initials: AR
authors.lastname: Muxworthy
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: András
authors.identifier: 0000-0001-8485-991X
authors.initials: A
authors.lastname: Kovács
authors.affiliation: School of GeoSciences, University of Edinburgh, The King's Buildings, West Mains Road, Edinburgh EH9 3JW, UK.
authors.forename: Wyn
authors.initials: W
authors.lastname: Williams
authors.affiliation: Department of Mechanical, Materials and Manufacturing Engineering, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
authors.forename: Paul D
authors.initials: PD
authors.lastname: Brown
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, D-52425 Jülich, Germany.
authors.forename: Rafal E
authors.initials: RE
authors.lastname: Dunin-Borkowski
mesh_terms: D018534:Earth, Planet; D052203:Ferrosoferric Oxide / Q000737:chemistry*; D060526:Magnetic Fields; D008280:Magnetics; D013696:Temperature
chemical_list: D052203:Ferrosoferric Oxide
keywords: Palaeomagnetism; in situ transmission electron microscopy; magnetite; nanoparticles; off-axis electron holography; pseudo–single-domain states; thermo-remanent magnetisation; thermomagnetic behavior