Winner: Ualisson Donardelli Bellon

University of Edinburgh.

Title: From microscopic minerals to planetary magnetic fields

Abstract:

Magnetic minerals are ubiquitous, they occur in the rocks, soils, and even the dust of all rocky planets and meteorites in our Solar System. These minerals can record, in the form of remanent magnetisation, information about the intensity and direction of ancient magnetic fields. Such records allow us to track continental motions through deep time and to investigate the complex dynamics of planetary molten cores. For decades, palaeomagnetists have relied on Néel’s Nobel Prize–winning theory of uniformly magnetised single-domain particles. However, it is now clear that many of the most stable carriers of magnetic remanence are actually non-uniformly magnetised particles in so-called vortex states. Thanks to the efforts of a small but active community, micromagnetic modelling has made substantial advances in closing this theoretical gap and improving the foundations of palaeomagnetic science.

Micromagnetic modelling allows us to investigate how vortex magnetic structures behave under varying conditions of temperature, pressure, and magnetic-field intensity (conditions where Néel’s theory often breaks down). This helps explain why experimental palaeointensity determinations fail at rates exceeding 80%. Yet there are limits to how far these insights can be applied when classical palaeomagnetic experiments rely on bulk measurements that average the signals of millions to billions of grains. 

The recent emergence of magnetic microscopy has changed this landscape. Technologies such as quantum diamond microscopy (QDM) now enable us to measure the magnetic signals of individual particles in microscopic samples, allowing us to perform more accurate and robust palaeomagnetic investigations.

In this lecture, I will outline how we are rapidly paving the way towards this new era of palaeomagnetic analysis. I will present results from numerical models showing how even a small number of vortex-state particles can accurately record magnetic fields, supporting the use of magnetic microscopy on microscopic return samples from space missions to study the magnetism of the Moon, Mars, and the early solar nebula. I will also discuss how high-resolution synchrotron nanotomography allows us to observe nanoscopic magnetic particles directly and to integrate these observations with micromagnetic modelling for the interpretation of magnetic microscopy data. Finally, I will describe our efforts to establish a framework for single-particle palaeointensity, bridging magnetic microscopy with micromagnetic modelling, and enabling the study of complex palaeomagnetic histories from the earliest stages of planetary evolution with unprecedented detail.

As part of the award, The British Geophysical Association has funds to cover the associated expenses for a number of these lectures.
If you would like the Bullerwell Lecture to be given at your institution, please contact Ualisson directly, cc the BGA President.