The revolution in spintronics technology can only be a heap away

A decade ago, the discovery of brush particles called magnetic skyrmions provided important new clues as to how microscopic spin textures would enable spin electronics, a new class of electronics that used the orientation of an electron’s spin rather than charge to store data. code.

But although scientists have made great strides in this very young field, they still do not quite understand how to design spintronics materials that make ultra-small, fast, low-power devices possible. Skyrmions may look promising, but scientists have long treated skyrmions only as 2D objects. However, recent studies have suggested that 2D skyrmions may actually be the origin of a 3D spinning pattern called hopfions. But no one could experimentally prove that magnetic hop fions exist on the nanoscale.

Now a team of researchers with Berkeley Lab has reported Nature communication the first demonstration and observation of 3D hopfions arising from skyrmions on the nanoscale (billionths of a meter) in a magnetic system. The researchers say that their discovery is an important step forward in the realization of high-density, high-speed, yet ultra-stable magnetic memory devices that harness the intrinsic power of electron spin.

“Not only have we proven that intricate turning structures such as 3D hopfions exist; we have also shown how to study them and exploit them,” says fellow senior author Peter Fischer, a senior scientist in the Materials Science Division. of Berkeley Lab, who is also an assistant professor of physics at UC Santa Cruz. “To understand how hopfions really work, we need to know how to make them and study them. This work was only possible because we have these amazing tools at Berkeley Lab and our collaborative partnerships with scientists around the world,” he said. said.

According to previous studies, hopfions, unlike skyrmions, do not float when moving along a device and are therefore excellent candidates for data technologies. Furthermore, collaborators of theories in the UK predicted that hopfions could originate from a multilayer 2D magnetic system.

The current study is the first to put the theories to the test, Fischer said.

Using nanofabrication tools at Berkeley Lab’s Molecular Foundry, Noah Kent, a Ph.D. student in physics at UC Santa Cruz and in Fischer’s group at Berkeley Lab, worked with Molecular Foundry staff to cut magnetic nanopillars from low iridium, cobalt, and platinum.

The more layered material was prepared by UC Berkeley’s postdoctoral fellow Neal Reynolds, under the supervision of fellow senior author Frances Hellman, who holds titles as a senior scientist in the Materials Science Division of Berkeley Lab, and Professor of Physics and Materials Science and Engineering. to UC Berkeley. She also leads the Department of Energy’s Non-Equilibrium Magnetic Materials (NEMM) program, which supported this study.

Hopfions and skyrmions exist as magnetic materials, but they have a distinctive twist pattern in three dimensions. To distinguish them, the researchers therefore used a combination of two advanced magnetic X-ray microscopy techniques – X-PEEM (X-ray photo-emission electron microscopy) at Berkeley Lab’s synchronous user setting, the Advanced Light Source; and magnetic soft X-ray transmission microscopy (MTXM) at ALBA, a synchrotron light facility in Barcelona, ​​Spain – to represent the clear spinning patterns of hopfions and skyrmions.

To confirm their observations, the researchers then performed detailed simulations to mimic how 2D screens in a magnetic device evolve into 3D hopfions in carefully designed multilayer structures, and how they will appear when polarized by X-rays. be imagined.

“Simulations are an extremely important part of this process, enabling us to understand the experimental images and design structures that will support hopfions, skyrmions, or other designed 3D spin structures,” Hellman said.

To understand how hopfions will eventually function in a device, the researchers plan to use Berkeley Lab’s unique capabilities and world-class research facilities – which Fischer describes as ‘essential for performing such interdisciplinary work’ – to explore the dynamic behavior of the to further study quixotic quasiparticles. .

“We have known for a long time that spider textures are almost inevitably three-dimensional, even in relatively thin films, but direct imaging was experimentally challenging,” Hellman said. “The evidence here is exciting and it opens doors to find and explore even more exotic and potentially significant 3D spin structures.”