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How does the Earth generate its magnetic field? While the basic mechanisms seem to be understood, many details remain unresolved. A team of researchers from the Center for Advanced Systems Understanding at the Helmholtz-Zentrum Dresden-Rossendorf, Sandia National Laboratories (USA) and the French Alternative Energies and Atomic Energy Commission has introduced a simulation method that promises new insights into the Earth’s core. The method, presented in PNAS, simulates not only the behavior of atoms, but also the magnetic properties of materials. The approach is significant for geophysics and could support the development of neuromorphic computing — an approach to more efficient AI systems.
The Earth’s magnetic field is essential for sustaining life, as it shields the planet from cosmic radiation and solar wind. It is generated by the geodynamo effect. “We know that the Earth’s core is primarily composed of iron,” explains Attila Cangi, Head of the Machine Learning for Materials Design department at CASUS. “As you get closer to the Earth’s core, both temperature and pressure increase. The increase in temperature causes materials to melt, while the increase in pressure keeps them solid. Because of the specific temperature and pressure conditions inside the Earth, the outer core is in a molten state, while the inner core remains solid.” Electrically charged, liquid iron flows around the solid inner core driven by Earth’s rotation and convection currents. These movements produce electric currents, which, in turn, generate the planet’s magnetic field.
However, important questions about the Earth’s core remain unanswered. For instance, what is the exact structure of its core? And what role do additional elements — thought to be present alongside iron — play? Both factors could profoundly influence the geodynamo effect. Clues come from experiments where scientists send seismic waves through the Earth and measure their “echoes” with highly sensitive sensors. “These experiments suggest that the core contains more than just iron,” says Svetoslav Nikolov from Sandia National Laboratories, lead author of the study. “The measurements do not agree with computer simulations that assume a pure iron core.”
Simulating shock waves on the computer
The research team now achieved significant progress by developing and testing a new simulation method. The key innovation of the method called molecular-spin dynamics lies in the integration of two previously separate simulation approaches: molecular dynamics, which models atomic motion, and spin dynamics, which accounts for magnetic properties. “By combining these two methods, we were able to investigate the influence of magnetism under high-pressure and high-temperature conditions on length and time scales that were previously unattainable,” emphasizes CEA physicist Julien Tranchida. Specifically, the team simulated the behavior of two million iron atoms and their spins to analyze the dynamic interplay between mechanical and magnetic properties. The researchers also employed artificial intelligence (AI), using machine learning to determine force fields — interactions between atoms — with high precision. Developing and training these models required high-performance computing resources.
Once the models were ready, the researchers performed the actual simulations: the digital model of two million iron atoms, representative of the Earth’s core, was subjected to the temperature and pressure conditions found in the Earth’s interior. This was done by propagating pressure waves through the iron atoms, simulating their heating and compression. When the speed of these shock waves was lower, the iron remained solid and adopted different crystal structures. When the shock waves were faster, the iron became mostly liquid. In particular, the researchers found that magnetic effects significantly affect the material’s properties. “Our simulations agree well with the experimental data,” says Mitchell Wood, a materials scientist at Sandia National Laboratories, “and they suggest that under certain temperature and pressure conditions, a particular phase of iron could stabilize and potentially affect the geodynamo.” This phase, known as the bcc phase, has not been experimentally observed in iron under these conditions, only hypothesized. If confirmed, the results of the molecular-spin dynamics method could help resolve several questions about the geodynamo effect.
Driving energy-efficient AI
Beyond uncovering new details about the Earth’s interior, the method also has the potential to drive technological innovations in materials science. Both in his department and through external collaboration, Cangi plans to use the technique to model neuromorphic computing devices. This is a new type of hardware inspired by the way the human brain works, which could one day process AI algorithms faster and more energy-efficiently. By digitally replicating spin-based neuromorphic systems, the new simulation method could support the development of innovative, efficient hardware solutions for machine learning.
Data storage offers a second compelling avenue for further research: Magnetic domains along tiny nanowires could serve as storage media that are faster and more energy-efficient than conventional technologies. “There are currently no accurate simulation methods for either application,” says Cangi. “But I am confident that our new approach can model the required physical processes in such a realistic way, that we can significantly accelerate the technological development of these IT innovations.”
Dr. Attila Cangi | Head of Department Machine Learning for Materials Design
Center for Advanced Systems Understanding (CASUS) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR)
Phone: +49 3581 37523 52
Email: a.cangi@hzdr.de
S. Nikolov, K. Ramakrishna, A. Rohskopf, M. Lokamani, J. Tranchida, J. Carpenter, A. Cangi, M.A. Wood: Probing Iron in Earth’s Core with Molecular-Spin Dynamics, PNAS, 2024 (DOI: https://www.doi.org/10.1073/pnas.2408897121)
Structure of the Earth
B. Schröder/HZDR/NASA/Goddard Space Flight Center Scientific Visualization Studio
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