Making ferromagnets ready for ultrafast communication and computing technology

An international team led by researchers at the University of California, Riverside, has made an important breakthrough in how to enable and exploit ultrafast spin behavior in ferromagnets. The research, “Spin inertia and self-oscillations in ferromagnets,” is published in Physical review papers and highlighted as an editors’ suggestion, paves the way for ultra-high frequency applications.

Today’s smartphones and computers operate at gigahertz frequencies, a measure of how fast they operate, with scientists working to make them even faster. New research has found a way to achieve terahertz frequencies using conventional ferromagnets, which could lead to next-generation communication and computing technologies that operate a thousand times faster.

Ferromagnets are materials where the electron spins line up in the same direction, but these spins also oscillate around this direction, creating “spin waves”. These spin waves are essential to emerging computer technologies, playing a key role in information and signal processing.

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

“Interestingly, these interactions also cause spins to gain inertia, leading to another type of spin oscillation called nutation.”

Barsukov explained that nutation occurs at ultra-high frequencies, making it highly desirable for future computing and communication technologies. Recently, physicists’ experimental confirmation of the notional oscillation excited the magnetism research community, he said.

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

Barsukov and his team found that injecting a spin current of the “wrong” sign can excite nutational auto-oscillations.

“These self-sustained oscillations hold great promise for next-generation computing and communication technologies,” said co-author Allison Tossounian, until recently a graduate student in the Barsukov Group.

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

“We were able to reconcile spin current-driven dynamics and spin inertia,” he said. “We also found an isomorphism, a parallel, between spin dynamics in ferromagnets and ferrimagnets, which could accelerate technological innovation by exploiting synergies between these fields.”

In ferrimagnets, usually two antiparallel spin lattices have an unequal amount of spin. Materials with antiparallel spin gratings have recently received increasing interest as candidates for ultrafast applications, Barsukov said.

“But many technological challenges remain,” he said.

“Our understanding of eddy currents and materials engineering for ferromagnets has advanced significantly over the last few decades. Together with the recent confirmation of nutation, we saw an opportunity for ferromagnets to become excellent candidates for ultra-high frequency applications. Our study sets the stage for concerted efforts to explore optimal materials and design efficient architectures to enable terahertz devices.”