An international team of researchers from NIMS, the University of Tokyo, Kyoto Institute of Technology, and Tohoku University has discovered that ultrathin films of ruthenium dioxide (RuO2) exhibit altermagnetism. This property distinguishes RuO2 as a third fundamental category of magnetic materials, sparking growing interest in altermagnets. Such materials have the potential to overcome key limitations of current magnetic memory technologies, enabling faster and more compact data storage.

RuO2 Prospects in Magnetic Memory

Ruthenium dioxide has long been considered a promising candidate for altermagnetism—a recently proposed form of magnetism that differs from traditional types. Unlike standard ferromagnetic materials used in memory devices, which can easily record data under external magnetic fields but are susceptible to interference, altermagnets combine magnetic stability with the ability to electrically read information. Antiferromagnetic materials, while resistant to external influences, make electrical data reading difficult due to the mutual compensation of internal magnetic spins. Altermagnets promise to unite the advantages of both categories. However, previous experimental results for RuO2 were inconsistent, and producing high-quality thin films with uniform crystallographic orientation was a significant challenge.

Breakthrough in Creating Thin RuO2 Films

The research team overcame these obstacles by successfully growing thin RuO2 films with a single crystallographic orientation on sapphire substrates. Careful substrate selection and precise control of growth conditions allowed them to manage the formation of the crystal structure. Using X-ray magnetic linear dichroism, the scientists mapped the spin arrangement and magnetic order in the films, confirming the compensation of net magnetization (N-S poles). They also detected spin-split magnetoresistance—electrical resistance changed depending on spin direction—which served as electrical evidence of a spin-split electronic structure.

Significance of the Results and Future Research

The experimental data matched theoretical calculations of magnetocrystalline anisotropy, confirming that thin RuO2 films indeed display altermagnetism. These findings significantly strengthen RuO2’s potential for developing next-generation magnetic memory devices with high speed and data storage density.

Building on these achievements, the team plans to develop advanced magnetic memory technologies based on thin RuO2 films. Such devices could offer faster and more energy-efficient information processing thanks to the inherent speed and density of altermagnetic materials.

New Methods and Prospects for Spintronics

The magnetic analysis methods developed during this research, using synchrotron radiation, will help scientists identify and study other altermagnetic materials. This approach could accelerate progress in spintronics and open new possibilities for future electronic devices.