Bullerwell 2021 abstract

Winner: Lesleis Nagy, postdoctoral researcher at the Scripps Institution of Oceanography, University of California San Diego

Abstract:

The magnetic field is a fundamental feature of the Earth, and its structure gives usimportant information about the geological processes deep within our planet. Sincerocks can retain records of the Earth’s field over billions of years, they provide awindow into the past and can answer basic questions such as how our planet wasformed. The way in which rocks acquire information and the techniques used inthe laboratory to recover the ancient field is complicated by the fact that our un-derstanding of the small magnetic particles that hold the ancient field is incomplete.Néel’s single-domain (SD) theory has shaped our understanding of magnetic record-ing and forms the basis of current experimental methods used to extract palaeo-magnetic signals. However,despite its undeniable success, the theory is limited inthe sizes and morphologies it can explain and it has long since been recognized thatthe majority of magnetic minerals form particles that are too large to be uniformlymagnetized. These larger grains contain pseudo-single domains (PSD) and show arange of behaviors that are quite unexpected. For example, recent work has shownthat so-called single-vortex (SV) domain structures are not only significantly morecommon than SD, since they occupy a larger range of grain sizes, but are also sur-prisingly thermally stable. It has also been observed that as grain sizes increase andthe SD state evolves into the SV state, the transition is marked by an “unstablezone” – a region characterized by low blocking temperatures and coercivities, butan increase in the number of possible domain states that can be nucleated in thegrain.In this talk we explore how palaeomagnetic samples record information, in partic-ular the effect of SV grains on the acquisition and recovery of ancient planetary fields.

What is the current state of the art in our understanding of non-uniform recorders andwhat is the way towards fully characterizing the mechanisms by which rocks recordinformation?9

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