Today’s computers store information in magnetic hard drives, keeping files safe even when the device is powered off. But to run programs and process information, computers rely on electricity. Each calculation requires a transfer of information between the electric and magnetic systems. This back-and-forth is a major bottleneck in the speed of modern computing. 

Devices that integrate magnetic components directly into computing logic would remove this limitation and allow computers to perform faster and more efficiently. 

A new theoretical study led by University of Delaware engineers reveals that magnons, a type of magnetic spin wave, can produce detectable electric signals. The findings, appearing in Proceedings of the National Academy of Sciences, highlight potential ways to control and manipulate magnons with electric fields and suggest a path toward integrating electric and magnetic components to enable next-generation computing technologies. 

The work was conducted as part of UD’s Center for Hybrid, Active and Responsive Materials (CHARM), a Materials Research Science and Engineering Center funded by the National Science Foundation.

How magnetic waves carry information

Magnetism originates from electrons, tiny particles that orbit an atom’s nucleus. Each electron has a property called spin, which can point up or down. In a standard iron ferromagnet, all the spins point in the same direction, creating a magnetic field.

“Imagine there's a spring connecting all these spins. If I deflect one spin, it's like pulling on the spring. The next spin deflects, then the next one, then the next,” said senior author Matthew Doty, professor in the Department of Materials Science and Engineering at UD’s College of Engineering. “You can think of it like a slinky: stretch it and give it a twitch, and a wave propagates down the coil. A magnon is just like that: a wave.”

In today’s computer chips, charged electrons flow through wires, generating resistance and losing lots of energy as heat. Because magnons transmit information through the orientation of spins, without moving any electric charges, they do not face resistance and waste far less energy. 

The new study focused on antiferromagnetic materials, in which the spins alternate up and down. These materials are appealing for computing applications because magnons in antiferromagnets can propagate at terahertz frequencies, roughly a thousand times faster than the speed of magnons in ferromagnets. But because the overall spin in antiferromagnetic materials is zero, antiferromagnetic magnons are extremely difficult to detect and manipulate.

A path to detecting and manipulating magnons

CHARM postdoctoral researcher D. Quang To and colleagues used computer simulations to explore how magnons behave in antiferromagnetic materials. To their surprise, the calculations revealed that the movement of magnons can generate electrical signals.

“The results predict that we can detect magnons by measuring the electric polarization they create,” said Doty. “Even more exciting is the possibility that we could use external electric fields, including those of light, to control the motion of magnons. Future devices that replace conventional wires with magnon channels could send information much faster and with much less wasted energy.”

The team started by analyzing what happens when one side of a material is hotter than the other, causing magnons to flow from hot to cold. In particular, they sought to understand the consequences of the orbital angular moment of magnons, a circular motion of the magnetic waves that is distinct from their forward movement. 

“We developed a mathematical framework to understand how orbital angular moment contributes to magnon transport,” said To, the paper’s first author. “We discovered that when the magnon orbital angular moment interacts with the atoms in the material, it produces an electric polarization.” 

In other words, moving antiferromagnetic magnons can generate a measurable voltage. 

“Our framework provides a powerful tool that will allow the research community to predict and manipulate the behavior of magnons,” said To.

The UD team has begun experiments to verify the predicted effects. They also plan to explore how magnons interact with light to determine whether the orbital angular moment of light can be used to control the transport or detection of magnons. 

This research is part of an interdisciplinary effort at CHARM focused on developing hybrid quantum materials for terahertz applications. 

Other co-authors of the paper include graduate student Federico Garcia-Gaitan, assistant professor Yafei Ren, associate professor M. Benjamin Jungfleisch, UNIDEL Professor John Q. Xiao and professor Branislav K. Nikolić of the Department of Physics and Astronomy in UD’s College of Arts and Sciences. UD Engineering professor Joshua Zide and Garnett W. Bryant, of the National Institute of Standards and Technology and the University of Maryland, College Park, are also co-authors. The work was primarily supported by NSF through the UD Materials Research Science and Engineering Center under award number DMR-2011824.