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In 2023, researchers at EPFL achieved a significant breakthrough by utilizing charge-free magnetic waves known as spin waves for data transmission and storage, as opposed to conventional electron flows. This advancement came from the Lab of Nanoscale Magnetic Materials and Magnonics, under the guidance of Dirk Grundler from the School of Engineering. The team used radiofrequency signals to invigorate spin waves, enabling them to reverse the magnetization states of tiny nanomagnets. This switching capability—from 0 to 1—facilitates the storage of digital information, vital for computer memory and various information and communication technologies.
This innovation marks a pivotal move towards sustainable computing. By leveraging spin waves, which involve quasiparticles referred to as magnons, the research aims to mitigate the energy losses—known as Joule heating—that are typically associated with electron-driven devices. However, previous efforts were hampered by the inability to reuse the magnetic bits for data overwriting.
Recent collaborative research led by Grundler’s lab and Beihang University, published in Nature Physics, has made strides in enabling such repeated data encoding. The teams reported astonishing magnetic properties within hematite, an iron oxide that is abundant and environmentally favorable compared to materials currently utilized in spintronic applications.
Grundler expressed: “Our findings signify that hematite is more than just a sustainable alternative to established materials like yttrium iron garnet. It unveils novel spin physics that can be employed for signal processing at exceptionally high frequencies, which is crucial for evolving ultrafast spintronic devices and their roles in next-generation information and communication technologies.”
Two magnon modes are superior to one
The revelation of these properties was serendipitous when EPFL alumnus Haiming Yu, now a professor at the Fert Beijing Institute and associated with the MIIT Key Laboratory of Spintronics at Beihang University, noticed unusual electrical signals emanating from a nanostructured platinum stripe on hematite. Researcher Lutong Sheng, from Yu’s team, found that these signals were unlike any previously recorded in standard magnetic materials, prompting them to send the device to Grundler’s lab for further examination.
Upon analyzing the magnon signals, Grundler detected an unusual ‘wiggle’ in their spatial distribution. “This sharp observation was a critical turning point, leading to the discovery of an interference pattern,” Yu articulated. Through light scattering microscopy, EPFL PhD student Anna Duvakina established that the peculiar electrical signals in the hematite sample correlated with interference patterns between two distinct spin wave excitations known as magnon modes.
Other magnetic substances, such as yttrium iron garnet, typically produce only a singular magnon mode, but the presence of dual magnon modes is advantageous. This configuration permits spin currents generated from magnons to toggle between opposite polarizations within the same device, facilitating bi-directional switching of a nanomagnet’s magnetization state. The researchers are optimistic about testing this theoretical model by integrating a nanomagnet onto the hematite device.
“Hematite has been recognized for millennia, yet its weak magnetism has limited its applications,” Grundler remarked. “Now, it surprises us by outperforming materials developed specifically for microwave electronics in the 1950s. This embodiment of science exemplifies how we can repurpose an ancient, earth-abundant material for contemporary applications, paving the way for a more efficient and sustainable approach in spintronics.”
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