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Micromagnetic modelling and multipole expansions from Micromagnetic Tomography
  • David Cortés-Ortuño,
  • Karl Fabian,
  • Lennart de Groot
David Cortés-Ortuño
Utrecht University

Corresponding Author:d.i.cortes@uu.nl

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Karl Fabian
Geological Survey of Norway
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Lennart de Groot
Utrecht University
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Micromagnetic Tomography (MMT) is a technique that combines X-ray micro tomography and scanning magnetometry data to numerically invert the surface magnetic signal for the magnetic potential of individual magnetic grains via their spherical harmonic expansion [1]. The dipole and higher order multipole moment solutions are uniquely determined, which has been proved in [2]. As a result, this method has allowed to analyze the signal of individual grains in rock samples and synthetic samples, thus providing a new pathway to study the rock magnetic properties of the remanent magnetization carriers [3]. Furthermore, the higher order multipole signals in the magnetic particles are an indication that the grains carry more complex magnetic orderings, such as multi-domain or vortex states. Therefore, these higher order moments can be used to constrain the magnetic configuration of the magnetic particles. In this work we review the multipole expansion method used by MMT. In addition, we show three dimensional micromagnetic modelling results to predict the multipole signal of magnetic particles in different local energy minimum magnetization states. We show that for certain grains it is possible to uniquely infer the magnetic configuration from the inverted magnetic multipole moments. This result is crucial to discriminate single-domain particles from grains in more complex configurations. Our investigation proves the feasibility to statistically select ensembles of magnetic grains with similar properties, such as the magnetic state, which is a step forward to find stable paleomagnetic recorders. [1] L. V. de Groot, K. Fabian, A. Béguin, P. Reith, A. Barnhoorn and H. Hilgenkamp. Determining Individual Particle Magnetizations in Assemblages of Micrograins. Geophysical Research Letters, 45(7):2995–3000, 2018. [2] K. Fabian and L. V. de Groot. A uniqueness theorem for tomography-assisted potential-field inversion. Geophysical Journal International, 216(2):760–766, 2018. [3] D. Cortés‐Ortuño, K. Fabian and L. V. De Groot. Single particle multipole expansions from Micromagnetic Tomography. Geochemistry, Geophysics, Geosystems, 22:e2021GC009663, 2021.