Abstract The magnetic properties of bulk RuO2 remain a subject of active debate, despite its pivotal rolein the emergence of altermagnetism. The latter is a novel paradigm in magnetic phases, charac-terized by the absence of net magnetization due to anti-parallel alignment of magnetic moments,yet displaying finite spin-splitting in the electronic band structure. This unique behavior unlocksopportunities for advanced applications in information technology devices. Recent experimental andtheoretical investigations suggest that bulk RuO2 , contrary to prior assumptions, is non-magnetic.In this work, we propose the fabrication of RuO2 ultrathin films to robustly stabilize the altermag-netic phase. Unlike their bulk counterparts, ultrathin films up to about 2nm thickness experiencesubstantial strain relaxation, leading to a dramatic impact on the electronic structure that triggersa transition towards an altermagnetic behavior, which mimics the impact of an artificially appliedHubbard-U correction to account for electronic correlations. Our results imply that the surfacesensitiveness of the probing experimental techniques is essential to sense the altermagnetic behavioremerging at RuO2 surfaces. Our findings promote the use and exploration of ultrathin films for therealization of spintronic devices based on altermagnets.
Brahimi et al. (2025) studied this question.