Kyushu University achieves current-induced magnetization reversal in sputtered magnetic insulator

Magnetic random access memory (MRAM), which retains information even when powered off, is expected to be a key solution for reducing power consumption in electronic devices, but improvements in energy efficiency during data writing have been needed. Thulium iron garnet (TmIG), a new magnetic insulator, is capable of low power consumption and high-speed control, and research on this is advancing worldwide. However, conventional fabrication methods have been limited to specialized techniques unsuitable for mass production.

An international joint research group led by Associate Professor Naoto Yamashita of the Faculty of Information Science and Electronics Engineering, Kyushu University, Doctoral Student Roselle Ngaloy and Professor Saroj P. Dash from Chalmers University of Technology, Professor Chun-Yeol You of DGIST (Daegu Gyeongbuk Institute of Science and Technology), and Assistant Professor Soobeom Lee of Shinshu University has developed a new manufacturing process that solves this issue. This represents an important step in bridging basic research and applied research for high-performance magnetic insulator memory technology. It is expected to accelerate R&D of new spintronic devices and contribute to realizing a sustainable information society. The research was published in npj Spintronics.

The international joint research group tackled the development of a process to fabricate high-quality TmIG thin films using on-axis sputtering, a technique commonly employed in MRAM mass production lines.

By precisely optimizing conditions such as gas flow rate and pressure during deposition and post-deposition heat treatment, they achieved high-quality TmIG thin films with atomically flat surfaces and ideal crystal structures for the first time using this industrial method. When the cross-section of the fabricated TmIG film was observed using a high-resolution transmission electron microscope, it was found that the atoms were arranged in alignment with the substrate's crystal structure. The TmIG had grown epitaxially, and a high-quality single crystal had been obtained.

Furthermore, the group created Hall devices by stacking this TmIG thin film with Pt and performing microfabrication. They demonstrated that applying small current pulses to the Pt layer enabled stable, repeatable magnetization reversal of the TmIG more than 100 times. Moreover, the current density required for this magnetization reversal (data writing) was as low as that of high-quality devices fabricated using conventional techniques such as PLD, confirming low power consumption.

This demonstrated successful fabrication of extremely high-quality TmIG films using methods suitable for mass production and showed that highly energy-efficient data writing is possible.

Currently, the research group is developing new functional devices that leverage the characteristics of magnetic garnets based on the manufacturing technology they have created. In the future, they aim to expand to in-memory computing, where computation is performed within memory, and realize spintronic devices for the post-MRAM era.

Yamashita commented: "TmIG is a material developed in Japan and has attracted worldwide attention following recent reports of high-speed, low-power magnetization reversal. We believe this achievement provides a solution to challenges that researchers around the world have been tackling. This is the result of discussions and cooperation with many collaborative researchers. Going forward, we will accelerate research toward creating new functions with industry-academia collaboration in mind."

Journal Information
Publication: npj Spintronics
Title: Deterministic spin-orbit torque switching of epitaxial ferrimagnetic insulator with perpendicular magnetic anisotropy fabricated by on-axis magnetron sputtering
DOI: 10.1038/s44306-025-00105-z