新しい磁気的挙動を示す金属酸化物を発見（New material behavior to improve speed and efficiency of technology）

2025-06-12 ミネソタ大学

＜関連情報＞

• https://cse.umn.edu/college/news/new-material-behavior-improve-speed-and-efficiency-technology
• https://www.pnas.org/doi/10.1073/pnas.2500831122

エピタキシャル歪みRuO2薄膜における金属性と異常ホール効果 Metallicity and anomalous Hall effect in epitaxially strained, atomically thin RuO2 films

Seung Gyo Jeong, Seungjun Lee, Bonnie Lin, +13 , and Bharat Jalan
Proceedings of the National Academy of Sciences  Published:June 11, 2025
DOI:https://doi.org/10.1073/pnas.2500831122

Significance

Materials challenges frequently constrain fundamental discoveries and the development of breakthrough technologies, underscoring the pivotal role of high‐quality synthesis in overcoming such barriers. Using hybrid molecular beam epitaxy, we demonstrate precise control over composition, thickness, and epitaxial strain in RuO₂ thin films, preserving metallicity and stabilizing magnetism down to unit cell level. We observed a robust anomalous Hall effect, revealing the emergence of strain-engineered magnetic states, supported by density functional theory calculations. By pinpointing epitaxial strain as the origin of magnetism in RuO₂ thin films, this work resolves recent debates and illustrates how atomic-scale synthesis and strain engineering can unlock intriguing quantum states and advance the design of functional materials for next-generation spintronics and quantum technologies.

Abstract

The anomalous Hall effect (AHE), a hallmark of time-reversal symmetry breaking, has been reported in rutile RuO₂, a debated metallic altermagnetic candidate. Previously, AHE in RuO₂ was observed only in strain-relaxed thick films under extremely high magnetic fields (~50 T). Yet, in ultrathin strained films with distinctive anisotropic electronic structures, there are no reports, likely due to disorder and defects suppressing metallicity thus hindering its detection. Here, we demonstrate that ultrathin, fully strained 2 nm TiO₂/t nm RuO₂/TiO₂ (110) heterostructures, grown by hybrid molecular beam epitaxy, retain metallicity and exhibit a sizeable AHE at a significantly lower magnetic field (< 9 T). Density functional theory calculations reveal that epitaxial strain stabilizes a noncompensated magnetic ground state and reconfigures magnetic ordering in RuO₂ (110) thin films. These findings establish ultrathin RuO₂ as a platform for strain-engineered magnetism and underscore the transformative potential of epitaxial design in advancing spintronic technologies.