A revolution in spintronics technology could only be one hopfion

April 8, 2021

(Nanowerk News) Ten years ago, the discovery of quasiparticles called magnetic skyrmions provided important new clues about how microscopic spin textures would enable spintronics, a new class of electronics that uses the orientation of the spin electron to direct data rather than its charge.

But although scientists have made great strides in this very young field, they still do not fully understand how to design spintronic materials that would allow for ultra-small, ultra-fast, low-power devices. Skyrmions may look promising, but scientists have long treated skyrmions as just 2D objects. However, recent studies suggest that 2D skyrmions could actually be the genesis of a 3D rotation pattern called hopfions. But no one could experimentally prove that magnetic hopfions exist at nanoscales.

Now a team of researchers co-led by the Berkeley Lab has reported Nature Communications (“Creation and observation of hopfions in magnetic multilayer systems”) the first demonstration and observation of 3D hopfions emerging from skyrmions at nanoscale in a magnetic system. The researchers say their discovery heralds a major step forward in realizing high-density, high-speed, low-power magnetic memory devices, and yet ultra-stable memory devices that harness the internal power of electron spins. The artist’s drawing of the characteristic 3D spin texture of a magnetic hopfion. Scientists from the Berkeley Laboratory created and observed 3D hopfions. The discovery could improve spintronics memory devices. (Image: Peter Fischer and Frances Hellman / Berkeley Lab)

?? Didn’t we just prove that there are complex spin textures like 3D hopfions ?? We also demonstrated how to learn and therefore use them, ?? said co-senior author Peter Fischer, a senior scientist in the Department of Materials Science at Berkeley Laboratory, who is also an associate professor of physics at UC Santa Cruz. ?? To understand how hopfions really work, we need to know how to make and study them. This job was only possible because we have these amazing tools in the Berkeley Lab and our collaborative partnership with scientists from around the world, ?? he said.

According to previous studies, hopfions, unlike skyrmions, do not get carried away when moving along the device and are therefore excellent candidates for data technologies. Furthermore, theoretical collaborators in the United Kingdom have predicted that hopfions could be formed from a multilayer 2D magnetic system.

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

Use of nanomaking tools in the molecular foundry Berkeley Lab, dr. Noah Kent, a physics student at UC Santa Cruz and Fischer Group in the Berkeley lab, worked with Molecular Foundry staff to carve magnetic nano columns from layers of iridium, cobalt and platinum.

The multi-layered materials were prepared by UC Berkeley postdoctoral fellow Neal Reynolds under the supervision of co-senior author Frances Hellman, who holds the degrees of senior faculty scientist in the Department of Materials Science at Berkeley Laboratory, and professor of physics and materials science and engineering at UC Berkeley. She also heads the Department of Energy for Non-Equilibrium Magnetic Materials (NEMM), which supported this study.

Hopfions and skyrmions are known to coexist in magnetic materials, but have a characteristic three-dimensional spin pattern. So to differentiate them, the researchers used a combination of two advanced magnetic X-ray microscopy techniques ?? X-PEEM (X-ray photoemission electron microscopy) at Berkeley Lab’s Synchrotron, an advanced light source; and magnetic soft microscopy for X-ray transmission (MTXM) at ALBA, a synchrotron light plant in Barcelona, ​​Spain ?? to show the different patterns of rotation of hopfions and skyrmions.

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

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

To understand how hopfions will ultimately work in the device, researchers plan to use the unique capabilities of the Berkeley Lab and world-class research capabilities. what does Fischer describe as “necessary to conduct such interdisciplinary work” ?? for further study of quixotic quasiparticles ?? dynamic behavior.

?? We have long known that spin textures are almost inevitably three-dimensional, even in relatively thin films, but direct imaging is an experimental challenge, ?? said Hellman. ?? The evidence here is exciting and opens the door to finding and exploring even more exotic and potentially significant 3D spin structures.