Preparing ferromagnets for ultra-fast communication and computing technology

An international team led by researchers at the University of California, Riverside, has made a significant breakthrough in how to enable and exploit the ultra-fast spinning behavior of ferromagnets. The research titled “Spin inertia and self-oscillations in ferromagnets” is published in Physical Examination Letters and highlighted as the editors’ suggestion, paves the way for ultra-high frequency applications.

Today’s smartphones and computers operate at gigahertz frequencies, a measure of their operating speed, and scientists are working to make them even faster. The new research has found a way to reach terahertz frequencies using conventional ferromagnets, which could lead to next-generation communications and computing technologies that operate a thousand times faster.

Ferromagnets are materials in which the electron spins align in the same direction, but these spins also oscillate around that direction, creating “spin waves.” These spin waves are crucial to emerging computing technologies, playing a key role in information and signal processing.

“As the spins oscillate, they experience friction due to interactions with electrons and the crystal lattice of the ferromagnet,” said Igor Barsukov, associate professor of physics and astronomy, who led the study.

“Interestingly, these interactions also cause spin inertia, leading to an additional type of spin oscillation called nutation.”

Barsukov explained that nutation occurs at ultra-high frequencies, making it highly desirable for future computing and communications technologies. Recently, experimental confirmation of nutational oscillations by physicists has excited the magnetism research community, he said.

“Modern spintronic applications manipulate spins using spin currents injected into the magnet,” said Rodolfo Rodriguez, first author of the paper, a former graduate student in Barsukov’s group and now a scientist at HRL Labs, LLC.

Barsukov and his team discovered that injecting a spin current with the “wrong” sign can cause nutational self-oscillations.

“These self-sustaining oscillations hold great promise for next-generation computing and communications technologies,” said co-author Allison Tossounian, until recently an undergraduate in the Barsukov group.

According to Barsukov, spin inertia introduces a second time derivative into the equation of motion, making certain phenomena counterintuitive.

“We managed to harmonize the dynamics induced by the spin current and the spin inertia,” he said. “We also found an isomorphism, a parallel, between the spin dynamics of ferromagnets and ferrimagnets, which could accelerate technological innovation by exploiting synergies between these fields.”

In ferrimagnets, two antiparallel spin networks usually have an unequal amount of spin. Materials with antiparallel spin networks have recently attracted growing interest as candidates for ultrafast applications, Barsukov said.

“But many technological challenges remain,” he said.

“Our understanding of spin currents and materials engineering for ferromagnets has advanced significantly over the past several decades. Coupled with the recent confirmation of nutation, we saw an opportunity for ferromagnets to become excellent candidates for “Our study sets the stage for concerted efforts to explore optimal materials and design efficient architectures to enable terahertz devices.”