Enhanced orbital torque efficiency in nonequilibrium Ru50Mo50(0001) alloy epitaxial thin films

Epitaxial thin films of fully nonequilibrium hcp-Ru_50Mo_50(0001) nanoalloys were prepared as a chemically disordered alloy, in which the intrinsic spin Hall effect is expected to be negligible. Structural analyses confirmed the epitaxial growth and atomic scale alloying of the films. In contrast to a tiny torque efficiency (ξ_DL) of ∼0.4% for Ru50Mo50/CoFeB, the ξ_DL for the Ru50Mo50/Ni heterostructure reached ∼30% with a long-range relaxation length. The apparent dependence of ξ_DL on the ferromagnetic layer can be attributed to the orbital Hall effect (OHE). Interestingly, a smaller ξ_DL was observed for Ru/Ni, suggesting that the nonequilibrium Ru_50Mo_50 enhances its OHE. Furthermore, the enhanced ξ_DL is maintained by inserting a Ru layer between the Ru_50Mo_50 and Ni layers, showing orbital transport through Ru. This finding illustrates potential applications of nonequilibrium nanoalloy films in spin orbitronics and contributes to getting insights into the understanding of the interrelationships between nanostructures and orbital transport properties.