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 RuO₂ 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 RuO₂(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 RuO₂(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 RuO₂. Besides the fundamental significance, these findings will advance the development of spintronics towards higher efficiency and lower power consumption.