Scientists at the U.S. Department of Energy's Brookhaven National Laboratory are working on ways to use the magnetic spins in nanoscale devices to build tiny signal-generating or receiving antennas. They’ve found that nanoscale magnetic vortices separated by an extremely thin layer of copper can be driven to operate in unison, potentially producing a powerful signal that could be used in a new generation of communications devices, computers and other devices.
"Almost all of today's electronic technology, from the light bulb to the smartphone, involves the movement of charge," said Brookhaven physicist Javier Pulecio, lead author of a study published in Nature Communications. "But harnessing spin could open the door for much more compact and novel types of antennas that act as spin wave emitters, signal generators--such as the clocks that synchronize everything that goes on inside a computer--as well as memory and logic devices."
The experiment uses very small magnetic discs, with a radius of just 500 nanometers and a thickness of just 25 nanometers--too small to support multiple magnetic domains. The spins parallel to the disc's surface rotate around a core, either clockwise or counter-clockwise and at the core the spins point out of the disc's surface, either up or down. This structure, a magnetic vortex, thus has four possible states, up or down and clockwise or counter-clockwise.
The core of the vortex can be moved around within the nanodisc by applying an electric current or an external magnetic field, behaving much like a particle. Apply certain high-frequency electromagnetic excitations can set the vortex core moving in a circular motion about the center of the disc. These circular motions, or oscillations, are what the Brookhaven scientists hope to use.
"Magnetic vortex-based oscillators can be tuned to operate at different narrowly defined frequencies, making them extremely flexible for telecommunications applications," Pulecio said. "They are also self-contained elements, about 100,000 times smaller than oscillators based on voltage instead of spin, so they could prove to be less expensive, consuming less electricity, and won't take up as much room on the device. That's especially important if you are talking about miniaturization for cell phones, wearable electronics, tablets, and so on."
Two magnetic vortices separated by a thin layer of copper allowed the oscillations in the two layers to synchronize. This is important because stacking layers could provide a way to overcome the power limitations of current vortex-based spintronic antennas.
"Magnetic vortices were one of the first observed magnetic quasi-particles and we are currently looking to expand our investigations to observe other newly discovered spin textures and how we might harness those," said Pulecio.
The Nature Communications article, Coherence and modality of driven interlayer-coupled magnetic vortices (abstract free, full text available for purchase) shows the eigenmodes of the vortex systems studied occurred between 100 MHz and 700 MHz. I'm not aware of any use of nanomagnet spintronics in consumer communications devices, but as research such as that being done by Javier Pulecio and other scientists at Brookhaven National Laboratory could pave the way to new RF devices quite different from those we're used to.
