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Conference paperValdez-Grijalva MA, Nagy L, Muxworthy AR, et al., 2016,
Domain structure of greigite (Fe3S4) in the SD to PSD regime
, 15th Castle Meeting -
Conference paperNagy L, Williams W, Fabian K, et al., 2016,
Thermoremanent magnetization in pseudo-Single domain grains
, 15th Castle Meeting -
Conference paperShah J, Muxworthy AR, Almeida TP, et al., 2016,
Determining the magnetic recording fidelity of chondrule dusty olivine
, 15th Castle Meeting -
Conference paperSupakulopas R, Muxworthy AR, Riishuus MS, et al., 2016,
High-latitude palaeomagnetic field behaviour during 3-7 Ma in Northern Iceland
, 15th Castle Meeting -
Conference paperWilliams W, Nagy L, Ó Conbhuí P, et al., 2016,
The Hunting of the ‘Psark' - 40 Years On
, 15th Castle Meeting -
Conference paperPenny C, Muxworthy AR, Fabian K, 2016,
The Curie temperature of magnetite nanoparticles (poster)
, 15th Castle Meeting -
Journal articleAlmeida TP, Muxworthy AR, Kovacs A, et al., 2016,
Direct observation of the thermal demagnetization of magnetic vortex structures in non-ideal magnetite recorders
, Geophysical Research Letters, Vol: 43, Pages: 8426-8434, ISSN: 1944-8007The 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 Fe3O4 particle (~ 250 nm in diameter) during in situ heating is achieved through the construction and examination of magnetic-induction maps. Step-wise demagnetization of the remanence-induced Fe3O4 particle upon heating to above the Curie temperature, performed in a similar fashion to bulk thermal demagnetization measurements, revealed 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 Fe3O4 particle exhibits thermomagnetic behavior comparable to a single-domain carrier, and thus vortex-states are considered reliable magnetic recorders for paleomagnetic investigations.
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Conference paperWilliams W, Nagy L, Fabian K, et al., 2016,
The Hunting of the ‘Psark' - 40 Years On
, Beijing Earth and Planetary Interior Symposium -
Conference paperBerndt T, Muxworthy AR, 2016,
Viscous Remanent Magnetization Dating of Floods
, Beijing Earth and Planetary Interior Symposium -
Conference paperNagy L, Williams W, Muxworthy AR, et al., 2016,
Thermomagnetic Stability in Pseudo Single Domain Grains (invited)
, EGU 2016 -
Conference paperBerndt T, Muxworthy AR, 2016,
Magnetic dating of storm floods, jökulhlaups and tsunamis
, EGU 2016 -
Conference paperDi Chiara A, Muxworthy AR, Trindade R, 2016,
Paleointensity of Proterozoic magmatic rocks from South America (poster)
, EGU 2016 -
Conference paperWilliams W, Nagy L, Fabian K, et al., 2016,
Evolution of magnetic domain structures from Pseudo-Single-Domain to Multidomain (poster)
, EGU 2016 -
Journal articleAlmeida T, Muxworthy AR, Kovacs A, et al., 2016,
Direct visualization of the thermomagnetic behaviour of pseudo-single-domain magnetite particles
, Science Advances, Vol: 2, Pages: 1-5, ISSN: 2375-2548The study of the palaeomagnetic signal recorded by rocks allows scientists to understand the 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 thermo-remanent behaviour 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, whilst 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, it is demonstrated that Fe3O4 grains containing vortex structures are indeed reliable recorders of palaeo-directional and -intensity information; and the presence of PSD magnetic signals does not preclude the successful recovery of palaeomagnetic signals.
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Journal articleShah J, Koppers AP, Leitner M, et al., 2016,
Palaeomagnetic evidence for the persistence or recurrence of geomagnetic main field anomalies in the South Atlantic
, Earth and Planetary Science Letters, Vol: 441, Pages: 113-124, ISSN: 1385-013XWe present a dataset of a full-vector palaeomagnetic study of Late Pleistocene lavas from the island Tristan da Cunha in the South Atlantic Ocean. The current day geomagnetic field intensity in this region is approximately 25 μT, compared to an expected value of ∼43 μT; this phenomenon is known as the South Atlantic geomagnetic Anomaly (SAA). Geomagnetic field models extending back to the last 10 ka find no evidence for this being a persistent feature of the geomagnetic field, albeit, all models are constructed from data which is particularly sparse in the southern hemisphere. New 40Ar/39Ar incremental heating dating indicates the studied lavas from Tristan da Cunha extruded between 90 and 46 ka. Palaeointensity estimations of eight lava flows made using the Thellier method yield an average palaeointensity of 18±6 μT and virtual axial dipole moment (VADM) of 3.1±1.2×1022 Am2. The lava flows demonstrate four time intervals comparable to the present day SAA, where the average VADM of the Tristan da Cunha lavas is weaker than the global VADM average. This suggests a persistent or recurring low intensity anomaly to the main geomagnetic field similar to the SAA existed in the South Atlantic between 46 and 90 ka.
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