Tuning Spin‐Orbit Torques Across the Phase Transition in VO2/NiFe Heterostructure. (17th January 2022)

• Record Type: Journal Article
• Authors: Kim, Jun‐young; Cramer, Joel; Lee, Kyujoon; Han, Dong‐Soo; Go, Dongwook; Salev, Pavel; Lapa, Pavel N.; Vargas, Nicolas M.; Schuller, Ivan K.; Mokrousov, Yuriy; Jakob, Gerhard; Kläui, Mathias
• Is Part Of: Advanced functional materials. Volume 32:Number 17(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-01-17
• Subjects: current‐induced spin‐orbit torque -- insulator‐metal transition -- spin‐torque ferromagnetic resonance -- vanadium dioxide; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adfm.202111555
• Languages: English
• ISSNs: 1616-301X

Abstract

Abstract: The emergence of spin‐orbit torques as a promising approach to energy‐efficient magnetic switching has generated large interest in material systems with easily and fully tunable spin‐orbit torques. Here, current‐induced spin‐orbit torques in VO2 /NiFe heterostructures are investigated using spin‐torque ferromagnetic resonance, where the VO2 layer undergoes a prominent insulator‐metal transition. A roughly twofold increase in the Gilbert damping parameter, α, with temperature is attributed to the change in the VO2 /NiFe interface spin absorption across the VO2 phase transition. More remarkably, a large modulation (±100%) and a sign change of the current‐induced spin‐orbit torque across the VO2 phase transition suggest two competing spin‐orbit torque generating mechanisms. The bulk spin Hall effect in metallic VO2, corroborated by the first‐principles calculation of the spin Hall conductivity σ SH ≈ − 10 4 ℏ e Ω − 1 m − 1, is verified as the main source of the spin‐orbit torque in the metallic phase. The self‐induced/anomalous torque in NiFe, with opposite sign and a similar magnitude to the bulk spin Hall effect in metallic VO2, can be the other competing mechanism that dominates as temperature decreases. For applications, the strong tunability of the torque strength and direction opens a new route to tailor spin‐orbit torques of materials that undergo phase transitions for new device functionalities. Abstract : Current‐induced spin‐orbit torques in VO2 /NiFe bilayer structures are investigated using spin‐torque ferromagnetic resonance. Large modulation (±100%) and a sign change of spin‐orbit torque is observed across the VO2 insulator–metal transition. Bulk spin Hall effect in metallic VO2, corroborates with first‐principles calculation, and self‐induced/anomalous torque in NiFe is thought to be responsible for the observed spin‐orbit torque sign reversal.