Researchers create ‘magnon switch’ on silicon

Technology News |
By Ally Winning

The researchers have developed a practical technique for controlling magnons, which are essentially waves that travel through magnetic materials and can carry information. To use magnons for information processing requires a switching mechanism that can control the transmission of a magnon signal through the device.

Previous approaches to this required the use of exotic and expensive substrates, as well as refrigeration. The new approach, however, enables elements to be built on the silicon that commercial chips are made from and operates efficiently at room temperature.

As a result, say the researchers, this new approach might be more readily employed by computer manufacturers.

“This is a building block that could pave the way to a new generation of highly efficient computer technology,” says team member Patrick Quarterman, a physicist at the NIST Center for Neutron Research (NCNR). “Other groups have created and controlled magnons in materials that do not integrate well with computer chips, while ours is built on silicon. It’s much more viable for industry.”

Magnons – also called spin waves – would harness the property of electron spin to transfer information. In a conventional processor circuit, electrons travel from one place to another, and their movement generates heat; a magnon, however, moves through a long string of electrons, which themselves do not need to travel.

Instead, each electron’s spin direction — which, say the researchers, is a bit like an arrow stretching through the axis of a spinning top — magnetically influences the spin direction of the next electron in line. Tweaking the spin of the first electron sends a wave of spin changes propagating down the string. Because the electrons themselves would not move, far less heat would result.

Because the electron string stretches from one place to another, the magnon can carry information as it travels down the string. In chips based on magnon technology, say the researchers, larger and smaller wave heights (amplitudes) could represent ones and zeros; and because the wave height can change gradually, a magnon could represent values between one and zero, giving it more capabilities than a conventional digital switch.

To demonstrate their approach, the researchers used a technique called neutron reflectometry to explore the magnetic behavior within their device, which consists of a multilayer of thin films atop a base of silicon. The neutrons revealed an unexpected but advantageous interaction between two of the thin film layers: Depending on the amount of magnetic field applied, the materials order themselves in different ways that could represent a switch’s “on” or “off” state, as well as positions between on and off — making it akin to a valve.

“As you lower the magnetic field, the direction switches,” says Yabin Fan, a postdoctoral associate in MIT‘s electrical engineering department. “The data is very clear and showed us what was happening at different depths. There’s a very strong coupling between the layers.”

The magnon switch, say the researchers, could find use in devices that do another sort of calculating as well. Conventional digital switches can only exist in either on or off states, but because the amplitude of the spin wave can change gradually from small to large, it is possible that magnons could be used in analog computing applications, where the switch has values lying between 0 and 1.

“That’s why we consider this to be more like a valve,” Quarterman said. “You can open or close it a bit at a time.”

For more, see “Manipulation of Coupling and Magnon Transport in Magnetic Metal-Insulator Hybrid Structures.”

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