Signals ride on waves of one kind or another: light, sound, radio. But new carriers are needed to relay information in next-generation devices. Disturbances or waves in magnetic materials called magnons could be an efficient option - if scientists can tame them.
A team led by researchers from the U.S. Department of Energy’s (DOE) Argonne National Laboratory and the University of Illinois Urbana-Champaign (U. of I.) has developed a method to generate spontaneous magnons in a material called yttrium iron garnet (YIG) that can be tuned to an external signal. The results, reported in Nature Communications, establish a pathway toward controllable magnons that are relevant for next-generation microelectronics, wireless communication and quantum information processing.
Researchers know how to generate magnons in magnetic thin films. Less is known about how to make those oscillations both spontaneous, or self-sustaining, and steadily rhythmic in response to an external cue. Achieving stable magnons means a new way for delivering and processing information in ways that other types of waves cannot.
“Parametric pumping usually creates chaotic wave motions, and it is hard to use the chaos for applications. With our method, we can create ultrasharp waves that are highly controllable.” - Yi Li, Argonne assistant scientist
To achieve this goal, the magnons are generated using a technique called parametric pumping. Think about parametric pumping as a person on a swing: By timing their motion with the swing’s natural rhythm, they can add energy without an external push. A similar principle is used to drive magnons.
The pumping method begins with a pair of microwave antennas on a YIG thin film a couple hundred nanometers thick, a tiny fraction of the width of a human hair. The small antenna dimensions enable scientists to control the generation of spontaneous oscillations with extreme precision.
The magnons are then tweaked with an outside signal, resulting in a phenomenon called phase-locking. This means the magnon can adapt itself to the external signal, similar to how two metronomes placed on the same surface fall into the same rhythm.
“Parametric pumping usually creates chaotic wave motions, and it is hard to use the chaos for applications,” said Yi Li, an assistant scientist at Argonne and one of the study’s lead authors. “With our method, we can create ultrasharp waves that are highly controllable.”
Generating stable, externally tunable magnons could be useful for next-generation electronics, where researchers are exploring ways to make computer chips ever more efficient. The study also connects to ongoing DOE-funded research at Argonne on hybrid quantum magnonics, where smart ways of processing magnon signals may find new potential in quantum circuits on chips. The work was funded by DOE’s Office of Science; by the U.S. National Science Foundation; by Argonne’s Laboratory Directed Research and Development project; and in part by Q-NEXT, a DOE National Quantum Information Science Research Center led by Argonne.
“We can now control the transition from those chaotic wave motions to tightly controlled, phase-locked, in-sync magnon oscillations,” said Argonne Distinguished Fellow Valentine Novosad, senior scientist and lead paper co-author.
The team demonstrated their setup in a classical, room-temperature system. But the controlled dynamics they observed are directly relevant to a different setting: hybrid superconducting-magnonic systems being developed for quantum information science through a DOE-funded project.
“We are exploring new physics and working to understand the building blocks of these future systems,” Novosad said.
The YIG component used in the study was fabricated and patterned in the clean room facilities at the Center for Nanoscale Materials, a DOE Office of Science user facility at Argonne.
“This work really highlights the benefits of an interdisciplinary national lab,” Novosad said. “When you have so much expertise on campus, including making and testing devices, it’s very powerful.”
The work also leverages the quantum prairie ecosystem of universities and other research organizations in the Midwest. The second author on the paper, Carissa Kiehl, is an undergraduate student whose work was funded by the Open Quantum Initiative as part of the Chicago Quantum Exchange, a research hub. And Axel Hoffmann, founder professor at U. of I.’s The Grainger College of Engineering and lead co-author of the paper, noted that his school’s connection with Argonne gives students and early-career researchers the chance to gain experience and interact with a national lab. One of those early-career scientists is Jinho Lim, a postdoctoral researcher in Hoffman’s lab at U. of I. and paper co-author.
Ongoing collaboration between Argonne and U. of I. set the stage for the paper, according to Hoffmann.
“We did not say, ’OK, let’s go look for this particular effect.’ It was more that we were trying to characterize microwave signals in these devices, and these signals popped up, leading us to drill down more,” he said. “The strength of fundamental science is that you can explore ideas.”
Now that the team has demonstrated that magnons can send and amplify signals at room temperature, the next step is to integrate these phenomena at the quantum limit.
“We are interested in exploring how this effect could be connected to an on-chip circuit or even a qubit,” Li said, referring to the fundamental unit of quantum information. “More broadly, this work provides a new way to generate and control coherent magnon signals, which could be useful for low-power microwave signal processing and future computing architectures.”