Spin‐Splitting Magnetoresistance in Altermagnetic RuO ₂ Thin Films

The recently discovered altermagnets, featured by the exotic correlation of magnetic exchange interaction and alternating crystal environments, have offered exciting cutting‐edge opportunities for spintronics. Nevertheless, the altermagnetism of RuO 2 , one of the earliest‐discovered altermagnets, is currently under intense debate. Here, this controversy is attempted to be resolved by demonstrating a spin‐splitting magnetoresistance (SSMR) effect that is driven by a spin current associated with the giant nonrelativistic spin splitting of an altermagnet. Compared to the spin Hall magnetoresistance induced by a conventional relativistic spin current, the SSMR is characterized by unusual angular dependence with a phase‐shift feature underpinned by the Néel‐vector orientation and pronounced temperature dependence caused by its susceptibility to electron scattering. Through systematical investigations on the magnetoresistance of (101)‐RuO 2 /Co bilayers, a sizable SSMR is disentangled and hence a Néel vector along [001] direction is unveiled. This work not only demonstrates a simple electric avenue for probing the Néel vector of altermagnets, but also indicates long‐range magnetic order in thin films of RuO 2 .