Press release from JGU partner about s-Nebula funded work on antiferromagnets (collaboration JGU/CNRS-Thales).

Physicists use antiferromagnetic rust to carry information over long distances at room temperature.

Be it with smartphones, laptops or mainframes: The transmission, processing and storage of information is currently based on a single class of material – as it was in the early days of computer science around 60 years ago. A new class of magnetic materials, on the other hand, could raise information technology to another level: Antiferromagnetic insulators enable computing speeds that are a thousand times faster than conventional electronics, with significantly less heating. Components could therefore be packed closer together and logic modules thus become smaller, a current limitation due to the increased heating of current components.

Information transfer at room temperature
So far, however, the problem was that the information transfer in antiferromagnetic insulators only worked at low temperatures. And nobody wants to have to put their smartphone in the freezer in order to use it. Physicists at JGU Mainz have now been able to eliminate this shortcoming, together with experimentalists from the CNRS / Thales Laboratory, CEA Grenoble and the National High Field Laboratory in France, as well as theorists from the Center for Quantum Spintronics (QuSpin) at the Norwegian University of Science and Technology. “In this novel result, we were able to transmit and process information in a standard antiferromagnetic insulator at room temperature – and over long enough distances to enable information processing to occur”, says Andrew Ross, scientist at JGU Mainz. The researchers used iron oxide (α-Fe2O3), the main component of rust, as an antiferromagnetic insulator, because iron oxide is widespread and easy to manufacture. The transfer of information in magnetic insulators is made possible by excitations of magnetic order known as magnons. These move as waves through magnetic materials – similar to how waves move across the water surface of a pond after a stone has been thrown into it. Previously, it was believed that these waves must have circular polarization in order to efficiently transmit information. In iron oxide, however, such circular polarization occurs only at low temperatures. However, the international research team was able to transmit magnons over exceptionally long distances even at room temperature. How did that work? “We have found: In antiferromagnets with a single plane, two magnons with linear polarization can overlap and migrate together – they complement each other to form an approximately circular polarization,” explains Dr. Romain Lebrun, Thales researcher at the joint CNRS/Thales laboratory in Paris who previously worked in Mainz. “The possibility of using iron oxide at room temperature makes it an ideal playground for the development of ultra-fast spintronic devices based on antiferromagnetic insulators.”

Extremely low attenuation – and therefore energy-efficient transmission
An important question in information transfer: How quickly is the information lost when moving through magnetic materials? This can be recorded quantitatively with the value of the magnetic damping. “The iron oxide examined has one of the lowest magnetic attenuations that has ever been reported in magnetic materials,” explains Professor Mathias Kläui from JGU Mainz. “We anticipate that high magnetic field techniques will show that other antiferromagnetic materials have similarly low attenuation, which is crucial for the development of a new generation of Spintronic devices. We are pursuing such low power magnetic technologies in a long term collaboration with our colleagues at QuSpin in Norway and I am happy to see that another piece of exciting work as come out of this collaboration.” The research was published as an article in the journal Nature Communications. The project was financed by the research and innovation program “Horizon 2020” of the European Union, the German Research Foundation (DFG) and the Norwegian Research Council.

For more information: R. Lebrun et al., “Long-distance spin-transport across the Morin phase transition up to room temperature in ultra-low damping single crystals of the antiferromagnet α-Fe2O3“, Nature Communications 11, Article number: 6332 (2020)