A Step Toward Next-Generation Low-Power Magnetic Memory
A research group from the Graduate School of Engineering at The University of Tokyo, in collaboration with Nippon Telegraph and Telephone Corporation (NTT), Japan Atomic Energy Agency (JAEA), Hokkaido University, and Kumamoto University, has successfully demonstrated current-induced magnetization switching in a ferromagnetic single layer of SrRuO3 (SRO), a material known as a Weyl semimetal. Typically, ferromagnet/heavy-metal bilayer structures have been used to generate a spin-orbit torque (SOT) that drives current-induced magnetization switching. However, in addition to the high cost of materials and fabrication, the critical current density required for switching (~107 A cm–2) is too high for practical applications. In the study of the research group, by analyzing the seemingly perfect periodic lattice of the SRO single layer, they revealed a barely discernible rotation of the RuO6 octahedral lattices (octahedra) on the order of ~10 pm (10–11 m) near the interface with the substrate. Theoretical calculations indicate that such a small displacement dramatically enhances the spin Hall effect, generating a strong enough SOT to enable magnetization switching even in a single ferromagnetic layer. Consequently, the research group successfully achieved a remarkably low critical switching current density of ~3.1 × 106 A cm–2 at 120 K, an order of magnitude smaller than that required in conventional bilayer systems. This discovery presents a novel strategy for designing spintronic materials: leveraging atomic-scale displacements in single crystals to enhance the SOT efficiency. This finding paves the way for the development of low-power, high-speed next-generation spintronic devices, such as magnetic memory and magnetic sensors, which are essential components in future technologies, including artificial intelligence (AI), neuromorphic computing, and autonomous driving systems.
Device operating principle based on experimental results: In the high-quality single-crystalline heterostructure of SrRuO₃/SrTiO₃ used in the experiments, it was revealed that the RuO₆ oxygen octahedra undergo slight rotations near the interface (white dashed line in the left panel) due to the difference in lattice parameters between SrRuO₃ and SrTiO₃. In this region, an applied charge current is converted into a spin current very efficiently by the enhanced spin Hall effect. The research group found that the resulting spin-orbit torque induces magnetization switching in SrRuO₃.
Papers
Journal: Advanced Materials
Title: Single-Layer Spin-Orbit-Torque Magnetization Switching due to Spin Berry Curvature Generated by Minute Spontaneous Atomic Displacement in a Weyl Oxide
Authors: Hiroto Horiuchi*, Yasufumi Araki*, Yuki K. Wakabayashi*, Jun’ichi Ieda, Michihiko Yamanouchi, Yukio Sato, Shingo Kaneta-Takada, Yoshitaka Taniyasu, Hideki Yamamoto, Yoshiharu Krockenberger, Masaaki Tanaka*, and Shinobu Ohya*
DOI: 10.1002/adma.202416091
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