Tuesday, November 15, 2016

Keeping Skyrmions on Track: the next (next) generation of electronics

The day after Halloween, gift guides started hitting mailboxes and inboxes. One of my favorite categories to browse is “For the tech-lover.” These lists feature the latest phones, smartwatches, and random novelties (like a wrist-band controlled BB-8). But even as people scan Black Friday ads for the best deal on the latest fitness trackers and virtual reality headsets, scientists are looking much further ahead—to the next, next generation of electronics.

I don’t mean the next generations of tablets and speakers, although that’s certainly true as well. I mean the next generations of the circuit components that form the backbone of all of these systems. In research published last week in the journal Physical Review B, a team of scientists from the Autonomous University of Barcelona in Spain provide insight on a particle-like feature that could be the future of electronics.

At a very basic level, our gadgets are controlled by electronic signals. These signals travel through circuit boards where they are read and manipulated by different components. In modern day circuits, the signal is transported by the charge of electrons. You have this technology to thank for every device within reach.

With the demand for smarter, faster, more energy-efficient devices, however, comes the need for new approaches that can do more in less space, in less time, and with less energy. In next generation electronics, the signal will likely be transported by the spin of an electron. In next, next generation electronics, scientists are looking to something called a skyrmion (skur-me-on) to transport the signal.
Skyrmions aren’t particles, but they act like particles. They are very small features that can be created in magnetic materials. In addition to being tiny, they are stable even at room temperature and are sensitive to very small amounts of current. These are ideal properties for the information carrier of the future.

A skyrmion is a pointlike region of reversed magnetization in a uniform magnet. The skyrmion’s “core”—here, pointed up—is surrounded by an axially symmetric twist that returns the spin texture to the background direction (down).
Image Credit & Caption: APS/Alan Stonebraker

Electrons travel through a circuit along conducting tracks, the silver lines that cover printed circuit boards. In order to use skyrmions for electronics applications, we need to be able to define their paths as well. Previous research has demonstrated that you can control skyrmions using magnetic tracks. However, if they get too close to a border—boom—they are annihilated.

In this new work, researchers Carles Navau, Nuria Del-Valle, and Alvaro Sanchez explored the physics of how skyrmions interact with the borders of these tracks. This has been studied in very specific cases, but not on a general level. Their result sheds light on how to design a track that keeps skyrmions safely moving in the right direction.

The researchers started by modeling the physical interaction between a skyrmion and border with mathematical equations. Next they solved these equations for different scenarios, such as current travelling parallel and perpendicular to the skyrmion. The trajectory of a skyrmion depends on its size and shape and the properties of the material, so the results were mathematical expressions.

To see whether their general expressions matched the results of the very specific cases studied by other research groups, the team put in the appropriate numbers for the size and shape of a skyrmion and the other parameters, and then calculated the results. Overall the tests showed that these expressions describe the behavior of skyrmions in a track well and that the model is a good one.

The researchers also looked at the interaction between skyrmions and borders when a skyrmion is trapped in a geometrically square region. This arrangement is important for applications such as tiny electrical oscillators. Under the right conditions, this geometry of the borders can actually boost the speed of the skyrmions inside.

The team has a long history of modeling superconductivity and has worked with magnetic structures for quite a while. Their interest in skyrmions evolved more recently. There was not a single moment of inspiration for this project, says Navau, rather the tools and ideas developed over a period of several months. Kind of like a pregnancy, he says—a topic not far from their minds as one of the co-authors welcomed a new baby recently. Speaking of babies, I would love to get a glimpse of what will be on the tech-lovers gift list for the next, next generation!

—Kendra Redmond

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