The rapid rise in AI applications has placed increasingly heavy demands on our energy infrastructure. All the more reason to find energy-saving solutions for AI hardware. One promising idea is the use of so-called spin waves to process information. A team from the Universities of Münster and Heidelberg (Germany) led by physicist Professor Rudolf Bratschitsch (Münster) has now developed a new way to produce waveguides in which the spin waves can propagate particularly far. They have thus created the largest spin waveguide network to date. Furthermore, the group succeeded in specifically controlling the properties of the spin wave transmitted in the waveguide. For example, they were able to precisely alter the wavelength and reflection of the spin wave at a certain interface. The study was published in the scientific journal Nature Materials.
The electron spin is a quantum mechanical quantity that is also described as the intrinsic angular momentum. The alignment of many spins in a material determines its magnetic properties. If an alternating current is applied to a magnetic material with an antenna, thereby generating a changing magnetic field, the spins in the material can generate a spin wave.
Spin waves have already been used to create individual components, such as logic gates that process binary input signals into binary output signals, or multiplexers that select one of various input signals. Up until now, however, the components were not connected to form a larger circuit. "The fact that larger networks such as those used in electronics have not yet been realized, is partly due to the strong attenuation of the spin waves in the waveguides that connect the individual switching elements — especially if they are narrower than a micrometer and therefore on the nanoscale," said Bratschitsch.
The group used the material with the lowest attenuation currently known: yttrium iron garnet (YIG). The researchers inscribed individual spin-wave waveguides into a 110-nanometer-thin film of this magnetic material using a silicon ion beam and produced a large network with 198 nodes. The new method allows complex structures of high quality to be produced flexibly and reproducibly.
The German Research Foundation (DFG) funded the project as part of the Collaborative Research Centre 1459 "Intelligent Matter."
Here is an exclusive Tech Briefs interview, edited for length and clarity, with Bratschitsch.
Tech Briefs: What was the biggest technical challenge you faced while creating this largest spin waveguide network to date?
Bratschitsch: There was not one big technical challenge. The biggest challenge was to solve many and very different problems, ranging from sample design, nanofabrication, characterization, simulations, to electrical and optical measurements, etc.; all done with a team of very different levels of experience, ranging from experienced researchers to bachelor students.
Tech Briefs: Can you explain in simple terms how it works please?
Bratschitsch: The new idea is to use an ion beam to define the spin-wave waveguides instead of etching, as it has been done earlier. The ion beam creates a cladding of the waveguide by partly amorphizing the crystalline magnetic material.
Tech Briefs: Do you have any set plans for further research/work/etc.? If not, what are your next steps?
Bratschitsch: One goal is to make the networks even bigger to create large magnonic integrated circuits (MICs) and to explore the limits of the new ion beam fabrication technique.
Tech Briefs: Is there anything else you’d like to add that I didn’t touch upon?
Bratschitsch: Researchers should develop new energy-efficient hardware platforms now. They are desperately needed, and the demand will extremely rise because of AI.
Tech Briefs: Do you have any advice for researchers aiming to bring their ideas to fruition?
Bratschitsch: Work hard and follow your dreams. Don’t get discouraged by frequent mishaps, which are inevitable if you do research.
