title: Direct observation of the thermal demagnetization of magnetic vortex structures in nonideal magnetite recorders.
abstract: The thermal demagnetization of pseudo-single-domain (PSD) magnetite (Fe3O4) particles, which govern the magnetic signal in many igneous rocks, is examined using off-axis electron holography. Visualization of a vortex structure held by an individual Fe3O4particle (~250 nm in diameter) during in situ heating is achieved through the construction and examination of magnetic-induction maps. Stepwise demagnetization of the remanence-induced Fe3O4particle upon heating to above the Curie temperature, performed in a similar fashion to bulk thermal demagnetization measurements, revealed that its vortex state remains stable under heating close to its unblocking temperature and is recovered upon cooling with the same or reversed vorticity. Hence, the PSD Fe3O4particle exhibits thermomagnetic behavior comparable to a single-domain carrier, and thus, vortex states are considered reliable magnetic recorders for paleomagnetic investigations.
authors.affiliation: Department of Earth Science and Engineering Imperial College London, South Kensington Campus London UK; Now at School of Physics and Astronomy, Kelvin Building University of Glasgow Glasgow UK.
authors.forename: Trevor P
authors.initials: TP
authors.lastname: Almeida
authors.affiliation: Department of Earth Science and Engineering Imperial College London, South Kensington Campus London 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 Jülich Germany.
authors.forename: András
authors.initials: A
authors.lastname: Kovács
authors.affiliation: School of GeoSciences University of Edinburgh Edinburgh UK.
authors.forename: Wyn
authors.initials: W
authors.lastname: Williams
authors.affiliation: School of GeoSciences University of Edinburgh Edinburgh UK.
authors.forename: Leslei
authors.initials: L
authors.lastname: Nagy
authors.affiliation: School of GeoSciences University of Edinburgh Edinburgh UK.
authors.forename: Pádraig Ó
authors.initials: PÓ
authors.lastname: Conbhuí
authors.affiliation: Department of Physics Technical University of Denmark Kongens Lyngby Denmark.
authors.forename: Cathrine
authors.initials: C
authors.lastname: Frandsen
authors.affiliation: Department of Earth Science and Engineering Imperial College London, South Kensington Campus London UK.
authors.forename: Radchagrit
authors.initials: R
authors.lastname: Supakulopas
authors.affiliation: Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute Forschungszentrum Jülich Jülich Germany.
authors.forename: Rafal E
authors.identifier: 0000-0001-8082-0647
authors.initials: RE
authors.lastname: Dunin-Borkowski
keywords: magnetite; paleomagnetism; thermal demagnetization