Orbital Hall Effect in Epitaxial RuO₂ Thin Films

The orbital Hall effect (OHE) has attracted significant attention as a mechanism for generating orbital currents [1], capable of manipulating magnetization in adjacent layers without relying on spin-orbit coupling [2]. Recent studies on epitaxial IrO2 thin films [3] suggest that RuO2 may also exhibit strong orbital currents, making it a promising material for orbitronic and spintronic applications. Additionally, prior work on RuO2 has revealed unconventional spin torques, potentially arising from magnetic order within the material [4].



We have grown high-quality epitaxial RuO2 thin films on TiO2 substrates with various orientations, including (001), (100), (111), (110), and (101), using reactive DC magnetron sputtering. We performed spin-torque ferromagnetic resonance (STFMR) measurements to investigate the OHE. We will discuss the quantification and disentanglement of OHE-induced torque contributions from both spin-orbit coupling and magnetic effects. Given the general structural complexity of altermagnetic candidates, to which RuO2 belongs, our findings are key for understanding the role that orbital effects may play in the transport properties of this emergent class of materials.References:



[1] D. Go et al., EPL 135, 37001 (2021).

[2] D. Jo et al., Phys. Rev. Research 2, 013177 (2020).

[3] M. Patton et al., arXiv:2410.02996 (2024).

[4] G. Gurung et al., Nature Electronics 5, 267 (2022).