At Berlin's Max Born Institute, physicists have opened a new window into the quantum world of magnons—the invisible quanta that carry information through magnetic materials at speeds around 100 times faster than today's computer chips. The breakthrough is a technique called magnon momentum microscopy, which uses soft X-rays to watch these nanoscale spin waves in action, revealing how they interact and redistribute energy across momentum space in ways that could reshape the future of computing.
For decades, scientists have known that spins—the fundamental building blocks of magnets—aren't rigid or static. Coupled over comparatively long distances, they can be easily excited and exhibit wave-like dynamics, giving rise to spin waves. More recently, researchers have recognized magnons as potential game-changers for next-generation computing: unlike conventional electronics that process information through the flow of electrons, magnons could enable wave-based information processing, potentially reducing the energy losses that plague modern CPUs. But studying magnons at the nanometer scale—the wavelengths needed for integration into real devices—has remained a formidable experimental challenge.
The international team, led by researchers from the Max Born Institute in collaboration with the Helmholtz-Zentrum Berlin, the Università degli Studi di Napoli Federico II, and the École Polytechnique Fédérale de Lausanne, developed a powerful solution. Their magnon momentum microscopy technique, published in Nature Physics, uses resonant soft X-rays to directly detect short-wavelength magnons. In the experiment, magnons act as a dynamic diffraction grating for the X-rays. By analyzing the resulting diffraction pattern, researchers can determine magnon wavelengths and amplitudes across an entire two-dimensional sample in a single measurement—giving them unprecedented visibility into magnon dynamics across momentum space.
"We can now directly observe magnon properties and their full distribution in momentum space," says Steffen Wittrock, first author of the study. "This gives us a completely new level of access to magnon dynamics."
The method's elegance lies in its simplicity and versatility. It combines high sensitivity with rapid data acquisition and doesn't require complex nanostructuring of samples. It works with a wide range of excitation schemes, making it broadly applicable across many magnetic systems.
When the team used magnon momentum microscopy to investigate magnons in yttrium iron garnet—a prototypical magnetic material—they uncovered something striking. At high excitation strengths, magnons didn't simply propagate in a single direction. Instead, at the highest energies, they redistributed across momentum space in characteristic patterns that revealed strong nonlinear interactions. Most remarkably, the experiments showed an omnidirectional population of magnons forming an elliptical ring in momentum space. This pattern provided direct evidence of four-magnon scattering: a process where two magnons collide and generate two entirely new magnons with different propagation directions.
Salvatore Perna, who developed the theoretical framework for understanding these observations, explains that this represents a more general type of four-magnon scattering than previously understood. "It arises from a parametric instability of magnons at finite wave vectors, redistributing energy across many modes," he notes. The discovery opens new terrain for understanding how magnons behave when pushed to extreme conditions—knowledge that could prove essential as researchers develop magnon-based devices for future computing architectures.
With this new platform established, the door is now open to exploring nonlinear magnon physics at scales and speeds that were previously invisible.