Simultaneous High Charge‐Spin Conversion Efficiency and Large Spin Diffusion Length in Altermagnetic RuO2

Abstract Efficient spin sources with large spin Hall angle ( θ SH ) and long spin diffusion length ( λ SD ) are highly desired in the application of spintronic devices. However, due to strong spin‐orbit coupling, the two targets can hardly be achieved simultaneously in conventional relativistic spin sources, like heavy metals. Here, it is proven that collinear antiferromagnetic RuO 2 films are able to address this key issue and break the inverse relationship of θ SH versus λ SD . Based on spin torque‐ferromagnetic resonance and spin pumping measurements, the authors demonstrate that the θ SH of RuO 2 (100) films is 0.183, and the λ SD is over 12 nm being an order of magnitude longer than that of Pt, β‐W, and β‐Ta. Meanwhile, sizable λ SD is also obtained in spin current with out‐of‐plane spin polarization generated by RuO 2 (101) films. By conducting a control experiment, the nonrelativistic altermagnetic spin splitting effect (ASSE) is ascertained to be the crucial mechanism accounting for the simultaneous large θ SH and long λ SD in RuO 2 . Besides the fundamental significance, these findings will advance the development of spintronics towards higher efficiency and lower power consumption.