Fully Field‐Free Spin‐Orbit Torque Switching Induced by Spin Splitting Effect in Altermagnetic RuO₂

Abstract Altermagnetism, a newly identified class of magnetism blending characteristics of both ferromagnetism and antiferromagnetism, is emerging as a compelling frontier in spintronics. This study reports a groundbreaking discovery of robust, 100% field‐free spin‐orbit torque (SOT) switching in a RuO₂(101)/[Co/Pt]₂/Ta structure. The experimental results reveal that the spin currents, induced by the in‐plane charge current, flow along the [100] axis, with the spin polarization direction aligned parallel to the Néel vector. These z‐polarized spins generate an out‐of‐plane anti‐damping torque, enabling deterministic switching of the Co/Pt layer without the necessity of an external magnetic field. The altermagnetic spin splitting effect (ASSE) in RuO₂ promotes the generation of spin currents with pronounced anisotropic behavior, maximized when the charge current flows along the [010] direction. This unique capability yields the highest field‐free switching ratio, maintaining stable SOT switching even under a wide range of external magnetic fields, demonstrating exceptional resistance to magnetic interference. Notably, the ASSE‐dominated spin current is found to be most effective when the current is aligned with the [010] direction. The study highlights the potential of RuO₂ as a powerful spin current generator, opening new avenues for advancing spin‐torque switching technologies and other cutting‐edge spintronic devices.