Control of Spin–Orbit Torques by Interface Engineering in Topological Insulator Heterostructures

• Published in: Nano letters 2020-08, Vol.20 (8), p.5893-5899
• Main Authors: Bonell, Frédéric, Goto, Minori, Sauthier, Guillaume, Sierra, Juan F, Figueroa, Adriana I, Costache, Marius V, Miwa, Shinji, Suzuki, Yoshishige, Valenzuela, Sergio O
• Format: Article
• Language: English
• Subjects: Physics
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.0c01850

(Bi1–x Sb x )2Te3 topological insulators (TIs) are gathering increasing attention owing to their large charge-to-spin conversion efficiency and the ensuing spin–orbit torques (SOTs) that can be used to manipulate the magnetization of a ferromagnet (FM). The origin of the torques, however, remains elusive, while the implications of hybridized states and the strong material intermixing at the TI/FM interface are essentially unexplored. By combining interface chemical analysis and spin-transfer ferromagnetic resonance (ST-FMR) measurements, we demonstrate that intermixing plays a critical role in the generation of SOTs. By inserting a suitable normal metal spacer, material intermixing is reduced and the TI properties at the interface are largely improved, resulting in strong variations in the nature of the SOTs. A dramatic enhancement of a field-like torque, opposing and surpassing the Oersted-field torque, is observed, which can be attributed to the non-equilibrium spin density in Rashba-split surface bands and to the suppression of spin memory loss. These phenomena can play a relevant role at other interfaces, such as those comprising transition metal dichalcogenides.