How is the Earth’s magnetic field produced? While the fundamental principles are largely understood, many specific aspects remain unclear. A research team from the Center for Advanced Systems Understanding (CASUS) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Sandia National Laboratories in the USA, and the French Alternative Energies and Atomic Energy Commission (CEA) has developed a simulation technique that could shed new light on the Earth’s core. This method not only analyzes atomic behavior but also captures the magnetic characteristics of materials. This research is crucial for geophysics and may also assist in advancing future technologies, such as neuromorphic computing—which offers a revolutionary approach to more efficient artificial intelligence systems. The research findings are published in the journal PNAS.
The Earth’s magnetic field is vital for life as it protects the planet from harmful cosmic rays and solar wind. This magnetic field is created by the geodynamo process. “We know that the Earth’s core mainly consists of iron,” says Attila Cangi, who heads the Machine Learning for Materials Design department at CASUS. “As you get closer to the Earth’s core, both temperature and pressure rise. The increasing temperature leads to melting, while elevated pressure keeps materials solid. Because of the unique temperature and pressure conditions within the Earth, the outer core remains molten, and the inner core stays solid.” The flow of electrically charged liquid iron around the solid inner core, propelled by the Earth’s rotation and convection currents, generates electric currents, which are responsible for the planet’s magnetic field.
However, key questions regarding the Earth’s core still need answers. For example, what is the exact structure of the core? What role do other elements, believed to exist alongside iron, play? These factors could significantly impact the geodynamo process. Insights have emerged from experiments where scientists send seismic waves through the Earth and analyze their echoes using sensitive sensors. “These experiments indicate that the core contains more than just iron,” explains Svetoslav Nikolov from Sandia National Laboratories, the lead author of the study. “The measurements contradict the results of computer simulations which assume a core made purely of iron.”
Simulating Shock Waves Digitally
The research team made substantial progress by creating and testing a new simulation method called molecular-spin dynamics. This innovative method integrates two previously distinct simulation techniques: molecular dynamics, which models atomic movements, and spin dynamics, which focuses on magnetic properties. “By merging these methods, we were able to explore the effects of magnetism under extreme pressure and temperature conditions, reaching scales that were not possible before,” says CEA physicist Julien Tranchida. The team simulated the behavior of two million iron atoms and their spin characteristics to analyze the interrelationship between mechanical and magnetic properties. They also utilized artificial intelligence (AI) and machine learning to accurately determine atomic force fields—interactions among atoms—requiring powerful computing resources to develop and train these models.
After preparing the models, the researchers ran the actual simulations. The digital representation of two million iron atoms, reflective of the Earth’s core, was exposed to the extreme temperature and pressure conditions found within the Earth. This was achieved by sending pressure waves through the atoms to simulate heating and compression. When the speed of these shock waves was slower, the iron remained solid and formed different crystal structures. When the shock waves were faster, the iron transitioned to a mostly liquid state. Notably, the researchers discovered that magnetic influences considerably affect the material’s properties. “Our simulations align well with experimental data,” states Mitchell Wood, a materials scientist at Sandia National Laboratories. “They suggest that under certain temperature and pressure conditions, a specific phase of iron might stabilize, potentially influencing the geodynamo.” This phase, known as the bcc phase, has not yet been experimentally observed in iron under similar conditions, only hypothesized. If verified, the results from the molecular-spin dynamics method could help clarify several aspects of the geodynamo process.
Fueling Energy-Efficient AI
In addition to revealing new insights about the Earth’s interior, this method also holds promise for fostering advancements in materials science technology. Cangi plans to use this technique to model neuromorphic computing devices, a novel type of hardware inspired by human brain functionality that could enhance the speed and efficiency of AI algorithm processing. By digitally simulating spin-based neuromorphic systems, the new method could aid in the creation of innovative, energy-efficient hardware solutions for machine learning.
Data storage is another promising research area. Magnetic domains along tiny nanowires may serve as faster and more energy-efficient storage options than current technologies. “Presently, there aren’t any accurate simulation methods for these applications,” Cangi mentions. “But I believe our new approach can realistically model the necessary physical processes, significantly accelerating the technological progress in these IT innovations.”
