Hexagonal copper disk lattice enables spin wave control

A group of researchers from Tohoku University has potentially developed a method to control spin waves by creating a hexagonal pattern of copper disks on a magnetic insulator. The team’s research findings are expected to lead to greater efficiency and miniaturisation of communication devices in fields such as artificial intelligence (AI) and automation technology. The research findings were published in the journal Physical Review Applied.

In magnetic material, the spins of electrons are aligned. When these spins undergo coordinated movement, the movement generates a ripple in the magnetic order, dubbed spin waves. Spin waves generate little heat and offer many advantages for next-generation devices. Implementing spin waves in semiconductor circuits, which rely on electrical currents, could reduce power consumption and promote high integration. Since spin waves are waves, they tend to propagate in random directions unless controlled by structures and other means. As such, elements capable of generating, propagating, superimposing and measuring spin waves are being developed worldwide.

Taichi Goto, co-author of the research paper, said the researchers leveraged the wavelike nature of spin waves to directly control their propagation. “We did so by first developing an excellent magnetic insulator material called magnetic garnet film, which has low spin wave losses. We then periodically arranged small copper disks with diameters less than 1 mm on this film,” Goto said.

By arranging copper disks in a hexagonal pattern resembling snowflakes, the researchers could effectively reflect the spin waves. By rotating the magnonic crystal and changing the incident angle of spin waves, the researchers revealed that the frequency at which the magnonic band gap occurs remains unchanged in the range from 10 to 30 degrees. This suggests the potential for the two-dimensional magnonic crystal to control the propagation direction of spin waves.

Going forward, the researchers aim to demonstrate the direction control of spin waves using two-dimensional magnonic crystals and to develop functional components that utilise this technology.

Top image caption: An illustration of the two-dimensional magnonic crystal developed in this study, viewed from an oblique angle. Copper disks are periodically arranged on a magnetic garnet film. Image credit: Taichi Goto et al.