Neural networks are some of the most important tools in artificial intelligence (AI): they mimic the operation of the human brain and can reliably recognize texts, language and images, to name but a few. So far, they run on traditional processors in the form of adaptive software, but experts are working on an alternative concept, the ‘neuromorphic computer.’ In this case, the brain’s switching points—the neurons—are not simulated by software but reconstructed in hardware components. A team of researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now demonstrated a new approach to such hardware—targeted magnetic waves that are generated and divided in micrometer-sized wafers. Looking to the future, this could mean that optimization tasks and pattern recognition could be completed faster and more energy efficiently. The researchers have presented their results in the journal Physical Review Letters.
The team based its investigations on a tiny disc of the magnetic material iron nickel, with a diameter just a few micrometers wide. A gold ring is placed around this disc: When an alternating current in the gigahertz range flows through it, it emits microwaves that excite so-called spin waves in the disc. “The electrons in the iron nickel exhibit a spin, a sort of whirling on the spot rather like a spinning top,” Helmut Schultheiß, head of the Emmy Noether Group “Magnonics” at HZDR, explains. “We use the microwave impulses to throw the electron top slightly off course.” The electrons then pass on this disturbance to their respective neighbors—which causes a spin wave to shoot through the material. Information can be transported highly efficiently in this way without having to move the electrons themselves, which is what occurs in today’s computer chips.
Back in 2019, the Schultheiß group discovered something remarkable: under certain circumstances, the spin wave generated in the magnetic vortex can be split into two waves, each with a reduced frequency. “So-called non-linear effects are responsible for this,” explains Schultheiß’s colleague Lukas Körber. “They are only activated when the irradiated microwave power crosses a certain threshold.” Such behavior suggests spin waves as promising candidates for artificial neurons because there is an amazing parallel with the workings of the brain: these neurons also only fire when a certain stimulus threshold has been crossed.
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