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

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.