Generation, transmission, and conversion of orbital torque by an antiferromagnetic insulator
- Shilei Ding
- Paul Noël
- Gunasheel Kauwtilyaa Krishnaswamy
- Niccolò Davitti
- Giacomo Sala
- Marzia Fantauzzi
- Antonella Rossi
- Pietro Gambardella
2025-10-17
Electrical control of magnetization in nanoscale devices can be significantly improved through the efficient generation of orbital currents and their conversion into spin currents. In nonmagnetic/ferromagnetic bilayers, this conversion produces a torque on the magnetization, enabling magnetization switching and dynamic manipulation. While previous studies focus on metallic ferromagnets, we demonstrate a large orbital torque and enhanced orbital-to-spin conversion by an antiferromagnetic insulating CoO layer. Measurements in CuO x /CoO/Co trilayers show that inserting CoO reverses the torque’s sign and triples its magnitude compared to CuO x /Co. This behaviour stems from the inverted oxygen gradient at the CuO x /CoO interface and CoO’s high orbital multiplicity, which favours the transmission of orbital momenta and efficient orbital-to-spin conversion. At low temperatures, the onset of antiferromagnetic order induces a further many-fold increase of the torque, which we attribute to the efficient excitation and propagation of spin-orbit excitons induced by magnetic coupling. Comparative measurements of CuO x /NiO/Co and CuO x /MnO/Co trilayers show that the torque efficiency scales with the orbital momentum of the Co 2+ , Ni 2+ , and Mn 2+ ions in the antiferromagnet. These results reveal that antiferromagnetic insulators like CoO provide highly effective orbital-to-spin transduction, combining orbital torque and exchange bias functionalities to improve the performance of spintronic devices.