Altermagnetism Confirmed in RuO2 Thin Films-A Clear Path to Faster, Denser Memory
A collaborative team from NIMS, the University of Tokyo, Kyoto Institute of Technology, and Tohoku University has experimentally verified altermagnetism in ruthenium dioxide (RuO2) thin films. Their work, published in Nature Communications, positions RuO2 as a strong candidate for ultrafast, high-density memory that could benefit AI workloads and data-center infrastructure.
The key advance: they produced single-orientation RuO2 thin films and showed spin-dependent transport consistent with altermagnetic order. That combination-zero net magnetization with spin-split electronic states-directly addresses limits of today's ferromagnet-based memory.
Why current magnetic memory hits a wall
Ferromagnets make writing data straightforward, but stray magnetic fields create interference and restrict how tightly bits can be packed. Antiferromagnets resist external disturbances, yet their zero net magnetization makes electrical readout difficult.
Altermagnets promise the best of both: no net magnetization to reduce interference, plus symmetry-driven spin splitting that enables electrical readout. That is the prize-and RuO2 just took a major step toward it.
What the team actually did
The researchers fabricated single-variant RuO2(101) thin films on sapphire by aligning crystallographic axes through substrate choice and tuned growth conditions. This orientation control had been a sticking point worldwide and is critical for reproducible measurements.
They used X-ray magnetic linear dichroism (XMLD) to reveal a spin arrangement with canceling N-S poles, confirming no net magnetization. Transport tests then showed spin-split magnetoresistance-the electrical signature that resistance depends on spin orientation-verifying a spin-split electronic structure. First-principles calculations of magnetocrystalline anisotropy matched the experimental XMLD, closing the loop.
Why this matters for AI and data centers
Zero net magnetization limits stray-field crosstalk, supporting tighter bit densities. Spin-split bands enable electrical read/write schemes that could reach higher speeds with lower energy per operation.
If developed into devices, altermagnetic RuO2 could ease bottlenecks in memory bandwidth, latency, and energy-key constraints in large-scale AI training and inference.
- Material: Single-orientation RuO2(101) thin films grown on sapphire
- Measurements: XMLD confirmed spin order; transport showed spin-split magnetoresistance
- Theory: First-principles magnetocrystalline anisotropy aligned with experiment
- Outcome: Conclusive evidence of altermagnetism in RuO2 thin films
What to watch next
Orientation engineering looks pivotal for performance and device consistency. Expect efforts to prototype memory cells, test write schemes, and benchmark endurance and switching speed against ferromagnet-based MRAM alternatives.
The synchrotron-based magnetic analysis workflow used here should also accelerate the search for other altermagnets and guide spintronic device design.
Paper and funding
Study: "Evidence for single variant in altermagnetic RuO2(101) thin films," Nature Communications (24 September 2025). DOI: 10.1038/s41467-025-63344-y
Support: JSPS Grants-in-Aid for Scientific Research (22H04966, 24H00408); MEXT X-NICS (JPJ011438); GIMRT Program, Institute for Materials Research, Tohoku University; Cooperative Research Projects, Research Institute of Electrical Communication, Tohoku University.
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