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

Efficient spin sources with large spin Hall angle (theta(SH)) and long spin diffusion length (lambda(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 theta(SH) versus lambda(SD). Based on spin torque-ferromagnetic resonance and spin pumping measurements, the authors demonstrate that the theta SH of RuO2(100) films is 0.183, and the lambda(SD) is over 12 nm being an order of magnitude longer than that of Pt, beta-W, and beta-Ta. Meanwhile, sizable lambda 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 theta(SH) and long lambda(SD) in RuO2. Besides the fundamental significance, these findings will advance the development of spintronics towards higher efficiency and lower power consumption.