Faint Signals of Nanoscale Magnetism

Spin waves, also known as magnons, have been directly observed at the nanoscale. This breakthrough was made possible by combining a high–energy-resolution electron microscope with a theoretical method developed at Uppsala University. The results open exciting new opportunities for studying and controlling magnetism at the nanoscale.

"We could suddenly see all the magnons and every step of their dance at the nanoscale. Until now, only surface magnons had been glimpsed at this resolution. It was like getting front-row seats to a performance no one had ever seen in full," says José Ángel Castellanos-Reyes, co-first author of the study and researcher at Uppsala University.

The magnetism of materials such as iron and nickel is a consequence of "tiny magnets" attached to their atoms, so-called atomic spins. In these magnetic materials, the spins in different atoms dance together in a synchronized motion called spin waves or magnons.

Magnons play a key role in the rapidly growing research field of magnonics, where the spin waves are used to carry information instead of electric charges. Magnonics has the potential to drive the next generation of electronics, offering faster, smaller, and more energy-efficient technology compared to today's charge-based systems.

Despite their importance, magnons have been nearly impossible to observe at the nanoscale with existing technologies. A big challenge in magnonics is understanding how magnons behave and how their properties may be modified at the nanoscale. For example, until now it has not been possible to assess the effect of impurities, such as a vacancy where an atom is missing in a material, on the performance of magnonic devices.

But now, in a study published in Nature, researchers from Uppsala University and international collaborators have taken a big step forward by introducing a new method to visualize and analyze magnons at the nanoscale. This was possible thanks to the combination of experiments performed at SuperSTEM laboratory in the UK and two theoretical and computational methods developed at Uppsala University, TACAW and UppASD.

In the experiments, the researchers used a scanning transmission electron microscope (STEM) with extremely high energy resolution, around 7 meV, available in only a few instruments worldwide. They measured energy losses in the electron beam as it passed through the sample, revealing subtle traces of magnons.

The study shows that it is now possible to see how magnons behave at the nanoscale and could change how we understand magnetic materials.

"This is a milestone in magnonics and microscopy. It opens exciting opportunities for the development of spin-based electronic devices," says Castellanos-Reyes.

- Source: PHYS.ORG (By: Uppsala University, edited by Gaby Clark, reviewed by Andrew Zinin)

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