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Conference paperAbubakar R, Muxworthy AR, Sephton M, et al., 2015,
Mapping Petroluem Migration Pathways Using Magnetics and Seismic Interpretations (poster)
, AGU Fall 2015 -
Journal articleMuxworthy AR, 2015,
Investigation of magnetic particulate matter inside animals' lung tissue: preliminary results
, STUDIA GEOPHYSICA ET GEODAETICA, Vol: 59, Pages: 628-634, ISSN: 0039-3169- Author Web Link
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- Citations: 2
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Journal articleAlmeida TP, Muxworthy AR, Kasama T, et al., 2015,
Effect of maghemization on the magnetic properties of nonstoichiometric pseudo-single-domain magnetite particles
, Geochemistry Geophysics Geosystems, Vol: 16, Pages: 2969-2979, ISSN: 1525-2027The effect of maghemization on the magnetic properties of magnetite (Fe3O4) grains in the pseudo-single-domain (PSD) size range is investigated as a function of annealing temperature. X-ray diffraction and transmission electron microscopy confirms the precursor grains as Fe3O4 ranging from ~ 150 nm to ~ 250 nm in diameter, whilst Mössbauer spectrometry suggests the grains are initially near-stoichiometric. The Fe3O4 grains are heated to increasing reaction temperatures of 120 – 220 ºC to investigate their oxidation to maghemite (γ-Fe2O3). High-angle annular dark field imaging and localized electron energy loss spectroscopy reveals slightly oxidized Fe3O4 grains, heated to 140 ºC, exhibit higher oxygen content at the surface. Off-axis electron holography allows for construction of magnetic induction maps of individual Fe3O4 and γ-Fe2O3 grains, revealing their PSD (vortex) nature, which is supported by magnetic hysteresis measurements, including first order reversal curve analysis. The coercivity of the grains is shown to increase with reaction temperature up to 180 ºC, but subsequently decreases after heating above 200 ºC; this magnetic behavior is attributed to the growth of a γ-Fe2O3 shell with magnetic properties distinct from the Fe3O4 core. It is suggested there is exchange coupling between these separate components that results in a vortex state with reduced vorticity. Once fully oxidized to γ-Fe2O3, the domain states revert back to vortices with slightly reduced coercivity. It is argued that due to a core/shell coupling mechanism during maghemization, the directional magnetic information will still be correct, however, the intensity information will not be retained.
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Conference paperShah J, Muxworthy AR, Russell SS, et al., 2015,
USING MICRO-CT TO MAP METEORITIC MAGNETISM.
, 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, ISSN: 1086-9379 -
Conference paperShah J, Muxworthy AR, Almeida TP, et al., 2015,
VISUALIZING THE MAGNETIC BEHAVIOR OF CHONDRULE DUSTY OLIVINE USING ELECTRON HOLOGRAPHY.
, 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, ISSN: 1086-9379 -
Conference paperMuxworthy AR, Bland PA, Collins G, et al., 2015,
MAGNETIC FABRICS IN ALLENDE: IMPLICATIONS FOR MAGNETIC REMANENCE ACQUISITION.
, 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, ISSN: 1086-9379 -
Conference paperDi Chiara A, Muxworthy AR, Trindade R, 2015,
Palaeointensity of Proterozoic magmatic rocks from South America using the Preisach method, preliminary results
, IUGG 2015 -
Conference paperBerndt T, Muxworthy AR, Paterson G, et al., 2015,
Temperature and grain size dependence of the attempt time t0 for fine magnetic particles
, IUGG 2015 -
Conference paperBerndt T, Muxworthy AR, 2015,
Viscous remanent magnetization dating of cataclysmic floods in Iceland
, IUGG 2015 -
Journal articleMuxworthy AR, Williams W, 2015,
Critical single-domain grain sizes in elongated iron particles: implications for meteoritic and lunar magnetism
, Geophysical Journal International, Vol: 202, Pages: 578-583, ISSN: 1365-246XKamacite particles (Fe–Ni, Ni < 5 per cent), are very common in extra-terrestrial materials, such as meteorites. It is normally assumed that for kamacite particles to be reliable recorders of magnetic fields, they need to be magnetically uniform (single domain, SD) and thermally stable. Larger particles subdivide into non-uniform multidomain (MD) magnetic structures that produce weaker magnetic signals, while small SD particles become magnetically unstable due to thermal fluctuations and exhibit superparamagnetic behaviour. In this paper we determine the first micromagnetic calculation of the stable SD range domain-state phase diagram for metallic iron; previous calculations were analytical. There is a significant increase in the critical size for the SD/MD threshold size, for example, for cube-shaped iron particles, the critical SD/MD threshold has now been estimated to be 25 nm, compared to 17 nm for previous estimates. The larger critical SD/MD threshold size for iron, agrees better with previously published nanometric observations of domain state for FeNi particles, then early analytical models.
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Conference paperDøssing A, Muxworthy AR, Mac Niocaill C, et al., 2015,
Geomagnetic secular variation during 6-0.5 Ma: Paleomagnetic results from Eastern Iceland
, IUGG 2015 -
Conference paperMuxworthy AR, Heslop D, 2015,
Recovering Ancient Magnetic Field Intensities From Rocks Using FORC Measurements (poster)
, HMM2015 -
Journal articleDodd SC, Mac Niocaill C, Muxworthy AR, 2015,
Long duration (>4 Ma) and steady-state volcanic activity in the early Cretaceous Parana-Etendeka Large Igneous Province: New palaeomagnetic data from Namibia
, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 414, Pages: 16-29, ISSN: 0012-821X- Author Web Link
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- Citations: 51
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Journal articleDodd SC, Muxworthy AR, Mac Niocaill C, 2015,
Paleointensity determinations from the Etendeka province, Namibia, support a low-magnetic field strength leading up to the Cretaceous normal superchron
, GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, Vol: 16, Pages: 785-797, ISSN: 1525-2027- Author Web Link
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- Citations: 7
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Journal articleMuxworthy AR, Williams J, Heslop D, 2015,
Testing the use of viscous remanent magnetisation to date flood events
, Frontiers in Earth Science, Vol: 3Using erratics associated with large flood events, this paper assesses whether their viscous remanent magnetisation (VRM) can be used to date the flood events. We tested this method using flood erratics from three large events: (1) the Late Pleistocene Bonneville mega-flood in Idaho, USA, (~14–18 ka), (2) the 1918 A.D. Mt. Katla, Iceland, eruption and associated jökulhaup (meltwater flood) at Mýrdalssandur, and (3) the Markarfljót jökulhaup due to an earlier eruption of Mt. Katla (~2.5 ka). We measured 236 specimens, 66 of which yielded clear identifiable and measurable viscous magnetisation signals from erratics with clustered VRM directions. From the VRM unblocking temperatures, age estimates were made. The age estimate for the most recent event (Mýrdalssandur) worked well, with a median estimated age of 80 years (with individual erratic estimates distributed between 61–105 years) compared to the known age of 91 years. The ages of the other two events were over-estimated. The estimates for Markarfljót [15 ka (7–33 ka)] were based on the results of just one erratic. For the Bonneville flood the estimates were too old, however, this locality had the largest uncertainty in the ambient temperature used in the age determination; the VRM acquired is strongly dependent on the ambient temperature, the older the event the greater the uncertainty. Southern Idaho currently has hot summers, with average summer maximum temperatures of ~31°C, but a mean annual temperature of only ~ 9°C. It is suggested that the VRM dating method works best for recent events (<2–3 ka) where the ambient temperature history can be constrained.
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