Tuning Spin‐Orbit Torques Across the Phase Transition in VO<sub>2</sub>/NiFe Heterostructure
Jy Kim, Joel Cramer, Kyujoon Lee, Dong‐Soo Han, Dongwook Go, Pavel Salev, Pavel N. Lapa, Nicolás M. Vargas, Iván K. Schuller, Yuriy Mokrousov, G. Jakob, Mathias Kläui
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 VO 2 /NiFe heterostructures are investigated using spin‐torque ferromagnetic resonance, where the VO 2 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 VO 2 /NiFe interface spin absorption across the VO 2 phase transition. More remarkably, a large modulation (±100%) and a sign change of the current‐induced spin‐orbit torque across the VO 2 phase transition suggest two competing spin‐orbit torque generating mechanisms. The bulk spin Hall effect in metallic VO 2 , corroborated by the first‐principles calculation of the spin Hall conductivity , 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 VO 2 , 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.