DATE2025.09.24 #Press Releases

A New Magnetic State for the AI Era: Demonstrating “Alternating Magnetism” in Ruthenium Dioxide Thin Films

—Toward the Development of High-Speed, High-Density Memory for AI and Data Centers—

Summary

Background and Challenges
Ruthenium dioxide (RuO₂) has long been regarded as a promising candidate for exhibiting “altermagnetism,” the so-called third type of magnetism. Conventional ferromagnets can be easily written with external magnetic fields, but stray fields cause recording errors, posing a fundamental obstacle to high-density memory. Antiferromagnets are resistant to external disturbances such as stray fields; however, because atomic spins (N–S poles) cancel each other out, electrical readout is extremely challenging.

This created the demand for a new class of magnetic material that combines the best of both worlds—robustness against disturbances while still enabling electrical readout and, potentially, future rewriting. Yet, worldwide experimental results on RuO₂’s altermagnetism have been inconsistent, and the lack of high-quality thin films with uniform crystal orientation prevented definitive demonstration.

Key Achievements
A collaborative research team from NIMS, the University of Tokyo, Kyoto Institute of Technology, and Tohoku University succeeded in fabricating single-variant RuO₂ thin films with aligned crystal orientation on sapphire substrates. By optimizing substrate choice and growth conditions, the team clarified the mechanism that determines orientation.

Using X-ray magnetic linear dichroism (XMLD) measurements at the Photon Factory synchrotron facility of KEK, the researchers identified both the magnetic order—where total magnetization (N–S poles) cancels out—and the spin orientation. They further observed spin-split magnetoresistance, a phenomenon in which electrical resistance changes depending on spin orientation, thereby confirming electronic differences in spin states by electrical means.

These experimental results were consistent with first-principles calculations, providing conclusive evidence that RuO₂ thin films are indeed altermagnets. This establishes RuO₂ thin films as a highly promising candidate for next-generation high-speed, high-density memory devices.

Figure：Conceptual illustration of altermagnetism in single-variant RuO₂ thin films, showing XMLD signals and spin orientations.

Future Outlook
Building on this achievement, we aim to realize next-generation magnetic memory devices based on RuO₂ thin films that offer both high speed and high density. By leveraging the unique properties of altermagnetism, this technology is expected to contribute to energy-efficient information processing. In addition, the synchrotron-based magnetic analysis techniques established in this study can be applied to the exploration of other altermagnetic materials and to the development of spintronic devices.

The research findings were published in Nature Communications on September 24, 2025.

Associate Professor Jun Okabayashi of the Research Center for Spectrochemistry participated in this study as one of the corresponding authors.

Links

National Institute for Materials Science (NIMS) ,Kyoto Institute of Technology, Tohoku University

Journals

Journal name	Nature Communications
Title of paper	Evidence for single variant in altermagnetic RuO2(101) thin films
著者	Cong He, Zhenchao Wen*, Jun Okabayashi*, Yoshio Miura*, Tianyi Ma, Tadakatsu Ohkubo, Takeshi Seki, Hiroaki Sukegawa, and Seiji Mitani *Corresponding authors