Direct and Inverse Spin Splitting Effects in Altermagnetic RuO2

Abstract Recently, the altermagnetic materials with spin splitting effect (SSE), have drawn significant attention due to their potential to the flexible control of the spin polarization by the Néel vector. Here, the direct and inverse altermagnetic SSE (ASSE) in the (101)‐oriented RuO 2 film with the tilted Néel vector are reported. First, the spin torque along the x ‐, y ‐, and z ‐axis is detected from the spin torque‐induced ferromagnetic resonance (ST‐FMR), and the z ‐spin torque emerges when the electric current is along the 010 direction, showing the anisotropic spin splitting of RuO 2 . Further, the current‐induced modulation of damping is used to quantify the damping‐like torque efficiency ( ξ DL ) in RuO 2 /Py, and an anisotropic ξ DL is obtained and maximized for the current along the 010 direction, which increases with the reduction of the temperature, indicating the present of ASSE. Next, by way of spin pumping measurement, the inverse altermagnetic spin splitting effect (IASSE) is studied, which also shows a crystal direction‐dependent anisotropic behavior and temperature‐dependent behavior. This work gives a comprehensive study of the direct and inverse ASSE effects in the altermagnetic RuO 2 , inspiring future altermagnetic materials and devices with flexible control of spin polarization.