The revolution in spintronics technology is just a long way away

Ten years ago, the discovery of quasiparticles called magnetic skyrmions provided important new clues about how microscopic spin structures enable spintronics, a new class of electronics that uses the orientation of an electron’s spin instead of its charge to encode data.

But while scientists have made great strides in this very young field, they still don’t quite understand how to design spintronic materials that enable ultra-fast, ultra-fast, low-power devices. Skyrmions may seem promising, but scientists have long treated skyrmions as mere 2D objects. However, recent studies have suggested that 2D skyrmions may actually be the origin of a 3D spin pattern called hopfions. But no one could have proved experimentally that nanoscale magnetic hopfions exist.

Now, a team of researchers led by Berkeley Lab has reported in Nature Communications the first demonstration and observation of 3D hopfions emerging from nanoscale skyrmions (billionths of a meter) in a magnetic system. The researchers say their discovery represents a major step forward in realizing high-density, high-speed, low-power, yet ultra-stable magnetic memory devices that harness the intrinsic power of electron spin.

“Not only have we proven that complex spin textures such as 3D hopfions exist, we have also shown how to study and therefore exploit them,” said co-senior author Peter Fischer, a senior scientist in Berkeley’s Materials Sciences Division. Lab who is also an adjunct professor of physics at UC Santa Cruz. “To understand how hopfions really work, we need to know how to create and study them. This work was only possible because we have these great tools at Berkeley Lab and our partnerships with scientists around the world,” he said.

According to previous studies, unlike skyrmions, hopfions do not drift when they move past a device and are therefore excellent candidates for data technologies. In addition, theoretical staff in the UK had predicted that hopfions could arise from a multi-layer 2D magnetic system.

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

Using nanofabrication tools at Berkeley Lab’s Molecular Foundry, Noah Kent, a Ph.D. a physics student at UC Santa Cruz and in Fischer’s group at Berkeley Lab, collaborated with Molecular Foundry staff to create magnetic nanopilars from layers of iridium, cobalt and platinum.

The multi-layer materials were prepared by UC Berkeley postdoctoral scientist Neal Reynolds under the supervision of co-senior author Frances Hellman, who holds the title of senior faculty scientist in the Berkeley Lab’s Materials Sciences Division, and professor of physics and materials science and engineering at UC Berkeley. She also leads the Department of Energy’s Non-Equilibrium Magnetic Materials (NEMM) program, which supported this study.

Hopfions and skyrmions are known to co-exist in magnetic materials, but they have a characteristic spin pattern in three dimensions. To tell them apart, the researchers used a combination of two advanced magnetic X-ray microscopy techniques: X-PEEM (X-ray Photo Emission Electron Microscopy) at Berkeley Lab’s synchrotron user facility, the Advanced Light Source; and magnetic soft X-ray transmission microscopy (MTXM) at ALBA, a synchrotron light facility in Barcelona, ​​Spain – to image the different spin patterns of hopfions and skyrmions.

To confirm their observations, the researchers then ran detailed simulations to mimic how 2D skyrmions in a magnetic device evolve into 3D hopfions in carefully designed multilayer structures, and how they will appear when imaged with polarized X-ray light.

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

To understand how hopfions will ultimately function in a device, the researchers plan to use the unique capabilities and world-class research facilities of Berkeley Lab – which Fischer describes as “ essential to conducting such interdisciplinary work ” to transform the dynamic behavior. of the quixotic quasi-particles. .

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