NSFGEO-NERC: Transforming understanding of paleomagnetic recording: Insights from experimental observations and numerical predictions

Lead Research Organisation: University of Edinburgh
Department Name: Sch of Geosciences


Our understanding of the way in which rocks record the geomagnetic field is based on an analytical
theory which makes the assumption that particles are uniformly magnetized (i.e., they are single domain,
SD). But, it has long been known that most rocks contain grains referred to as pseudo-single-domain
(PSD); these are too big to be uniformly magnetized, and are unsuited for analytical theory.
Recent breakthroughs in numerical modeling have opened new avenues for understanding the nature of
PSD grains. Making it possible to estimate the temporal and thermal stability of PSD particles. This
approach has gained new urgency given recent results on PSD samples which call into question their
reliability for paleointensity research. The opportunity now exists to combine experimental and numerical
approaches for a radical new understanding of paleomagnetic recording, with the potential to transform
how paleointensity research is done.

Planned Impact

Who might benefit from this research?

This is a blue skies project where the end users are primarily within the academic community, but the project does have implications for the future development of industrial applications in the technology/hard drive sectors, in addition to the general public and schools.

How might they benefit from this research?

1. Industry
There is a large multi-national manufacturing industry concerned with the design and manufacture of high-stability and high-density magnetic data storage. Although much of the development in this area is driven by experimental innovation, there has been great interest over the last 20 years on initial magnetic materials design exploration using micromagnetic models. Much of the research being done micromagnetics in the Earth Science community has focused on non-ideal magnetic materials, temporal stability of the magnetic remanence, and the effects of thermal activation, appropriate to the range of magnetic materials in rocks and the principal methods by which they become magnetised. Whilst these developments are often not the immediate focus of current research in the industrial sector, it has often been the case that unexpected commercial innovations in data storage have benefited from the work done in the Earth Sciences. Indeed, an early example of the seminal paper by Louis Néel (1955) on 'Some theoretical aspects or rock magnetism', laid the foundation for our understanding of the stability of magnetic recordings in man-made recording materials that were being developed at that time. Our proposed research again addresses this most important question in the Earth Sciences of temporal and thermal stability of magnetic remanence. What we have already seen is that the 'non-deal' magnetic recording particles we have studied can often have higher thermal and temporal stability than the 'ideal' uniformly magnetised particles favoured in the industrial data-storage sector. There is a clear overlap, therefore, in the interest of the rock-magnetic community and commercial magnetic materials sector, in identifying magnetic particles of high stability and remanence.

The proposed project is perfectly positioned to enhance the engagement across the academic-industrial sector and across the earth and material science communities. We will aim to:

a) Bring the capabilities of the data-mining micromagnetic methodology to the wider attention of Earth and materials scientists both in academia and industry.

b) Provide a platform that will facilitate collaboration between the academic and commercial sector through free and simple access to a variety of modelling tools for simulating magnetic behaviour in bulk samples containing massive numbers of magnetic particles.

2. General public and Schools
This scientific background to this project is the need to provide evidence for some of the key
questions surrounding the evolution of the Earth and its magnetic field. This evidence not only defines the start of plate tectonics and the nucleation of the inner core, but also the emergence of the protective envelope of the geomagnetic field that provided an environment conducive to the emergence of life. These questions are all of interest to the general public.


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Valdez-Grijalva M (2018) Magnetic vortex effects on first-order reversal curve (FORC) diagrams for greigite dispersions in Earth and Planetary Science Letters

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Bellon U (2023) Unmixing of Magnetic Hysteresis Loops Through a Modified Gamma-Cauchy Exponential Model in Geochemistry, Geophysics, Geosystems

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Khakhalova E (2018) Magnetic Vortex States in Small Octahedral Particles of Intermediate Titanomagnetite in Geochemistry, Geophysics, Geosystems

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Nagy L (2019) From Nano to Micro: Evolution of Magnetic Domain Structures in Multidomain Magnetite in Geochemistry, Geophysics, Geosystems

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Mansbach E (2022) Size Ranges of Magnetic Domain States in Tetrataenite in Geochemistry, Geophysics, Geosystems

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Ó Conbhuí P (2018) MERRILL: Micromagnetic Earth Related Robust Interpreted Language Laboratory. in Geochemistry, geophysics, geosystems : G(3)

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Valdez-Grijalva M (2020) Micromagnetic simulations of first-order reversal curve (FORC) diagrams of framboidal greigite in Geophysical Journal International

Description This grant project has had remarkable success and we are just in the first few months of the award. The most significant finding is the the detailed understanding of what makes an ideal magnetic recorder of the ancient geomagnetic field. Hithertoo this was restricted to small uniformly magnetised particles, and we have now discovered that highly stable magnetic recorders can exist up to match larger grains containing distinctive vortex shaped magentization structures. This has revolutionised our understanding of paleomagnetic recording, and extended the size range of reliable palaeomagnetic recorders by an order or magnitude.

This means we can look at much more difficult geological problems: Extraterrestrial rocks that contain particles of iron or kamacite are thought to carry paleomagnetic recordings from the time of the formation of the Solar System. Interpretation of these recordings has hitherto falsely assumed particles were uniformly magnetized. We have reexamined the magnetic recording reliability of these minerals using numerical models that account for the more complex magnetic structures that are likely to exist and show that iron and kamacite particles are exceptionally good and thermally stable recorders of ancient magnetic fields, dominated by the recording made when iron cools through its Curie point. Additional recordings for thermal events that occur substantially below the Curie temperature will be difficult to extract from iron-dominated samples.

We have shown that the magnetic recording behaviour of non-uniformly magnetised nanoparticles have a distinctive character that can indemnify them, which involves looking at combination of the thermal stability and their response to demagnetising fields. The hope is that these characteristics can help isolate magnetic particles in a natural sample that retain reliable magnetic recordings over billions of years.

2022 Update:
During this last year we made a remarkable discovery that most naturally occurring magnetic materials have a magnetic anisotropy (preferred alignment of magnetisation) that is temperature dependent. This is a highly significant finding for palaeomagnetism, since it means that successive heating and cooling of a rock sample may not be able to regain the same magnetic intensity. In fact we have found that the intensity of thermally induced magnetic recording depends upon the complete thermal history of the sample and its cooling rate.
We are now able to simulate any arbitrary thermal history of a palaeomagnetic sample, and in particular we can simulate the laboratory experimental process of estimating palaeointensities. We have been able to demonstrate the cause of observed experimental artefacts that commonly cause such laboratory experiments to fail. In particular we can now understand the origin of 'partial Thermomagnetic Tails' (pTRM tails), where repeated attempts to remagnetise a material under apparently identical external environments, produce different results. Such an understanding is likely to have a profound impact on palaeointensity studies, and indeed to much wider applications of thermally assisted magnetisations, employed in magnetic recording media and medical applications.
Exploitation Route The grant will generate a massive online database of magnetic characteristics that will be open to the scientific community to allow them to asses the reliability of their experimental observations of paleomagnetic recordings.

We have been able to parametrise out model results to create a much more compact database of models with the intention of releasing a downloadable database of solution from which users can simulate any sequence of thermomagnetic experiments. We hope to be able to isolate the magnetic minerals, grain sizes and morphologies most affected by temperature dependent anisotropy, so that far more reliable palaeomagnetic estimates can be made. More reliable palaeointensities will better contain the thermal evolution of the deep Earth, the start of the geomagnetic field with implications for the evolution of life. Such an understanding then has implications for planetary evolution both in our own solar system and beyond.
Sectors Digital/Communication/Information Technologies (including Software),Environment,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology,Other

Description Summer School workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact This was a one day workshop on our open source micro magnetic modelling package. The workshop was given by invitation at the Institute of Rock Magnetism Summer School which occurs every two years at the University of Minnesota. It is sponsored by the National Science Foundation and provides training in rock and mineral magnetism to postgraduate students worldwide. It takes about 50 students in each summer school.
Year(s) Of Engagement Activity 2018