Geophysics seminar: Lesleis Nagy (SIO/GRD) "Understanding Palaeointensity Data using Micromagnetic Modelling"

11/27/2018 - 12:00pm to 1:00pm
Munk Conference Room
Event Description: 

Talk Abstract:

An accurate reconstruction of the historical behavior of the Earth’s magnetic field is an important aid to
understanding how it will evolve in the future. Additionally, such reconstructions offer us evidence of
continental drift, data to constrain geodynamo models and could even provide information about the
paleo-environment [1]. Unfortunately, recovery of accurate palaeointensities in the laboratory is an
extremely difficult task, with the main theoretical tool used by paleomagnetists for interpreting
observations being Neél’s single domain (SD) model [2], which is known to be limited when considering
the large range of shapes and sizes by which magnetic recorders are expressed in nature.
Recent work [3, 4] has shown that the single-vortex (SV) state is not only significantly more common than
SD, as it occupies a much larger range of grain sizes, but is also surprisingly thermally stable. As these
grains likely account for the majority of the signal measured in the laboratory, they must also be
responsible for the range of observations that lead to large inaccuracies in palaeointensity
measurements. Additionally, if we have a clear understanding of the SV state, we can more accurately
predict cooling rate adjustments for time scales not measurable in the laboratory, and find a physical link
between magnetic coercivity and blocking temperature.
In this presentation I intend to discuss the measurement of palaeointensities in an historical context along
with the work that we have completed so far. I focus on examining the role of the SV state in
palaeointensity measurements and our intended future research – a framework of computational tools for
paleomagnetists that will allow interpretations of measurements in light of advances in numerical

[1] Moisescu, C., Ardelean, I. and Benning, L.G., 2014. The effect and role of environmental conditions on
magnetosome synthesis. Frontiers in microbiology, 5, p.49.
[2] Neel, L., 1949. Theory of the magnetic after-effects in ferromagnetics in the form of small particles,
with applications to baked clays. Ann. Geophys, 5, pp.99-119.
[3] Nagy, L., Williams, W., Muxworthy, A.R., Fabian, K., Almeida, T.P., Conbhuí, P.Ó. and Shcherbakov,
V.P., 2017. Stability of equidimensional pseudo–single-domain magnetite over billion-year
timescales. Proceedings of the National Academy of Sciences, 114(39), pp.10356-10360.
[4] Nagy, L., Williams, W., Tauxe, L., Muxworthy, A.R., Ferreira, I. Thermomagnetic recording fidelity of
nanometer sized iron: implications for planetary magnetism (in review)

For more information on this event, contact: 
Michael Murphy
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