Tuning spin-orbit torques across the phase transition in VO${}_2$/NiFe heterostructure

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 were investigated using spin-torque ferromagnetic resonance, where the VO${}_2$ layer undergoes a prominent insulator-metal transition. A roughly two-fold increase in the Gilbert damping parameter, $\alpha$, with temperature was attributed to the change in the VO${}_2$/NiFe interface spin absorption across the VO${}_2$ phase transition. More remarkably, a large modulation ($\pm$100%) and a sign change of the current-induced spin-orbit torque across the VO${}_2$ phase transition suggest two competing spin-orbit torque generating mechanisms. The bulk spin Hall effect in metallic VO${}_2$, corroborated by our first-principles calculation of spin Hall conductivity, ${\sigma }_{SH}\approx 10^4\frac{\hslash }{e}{\Omega }^{-1}{m}^{-1}$, is verified as the main source of the spin-orbit torque in the metallic phase. The self-induced/anomalous torque in NiFe, of the opposite sign and a similar magnitude to the bulk spin Hall effect in metallic VO${}_2$, could 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 which undergo phase transitions for new device functionalities.

16 pages, 5 figures

References in corpus (5)

• Electrical Detection of Spin Transport in Lateral Ferromagnet-Semiconductor Devices
• Highly efficient and tuneable spin-to-charge conversion through Rashba coupling at oxide interfaces
• Theory of Current-Induced Angular Momentum Transfer Dynamics in Spin-Orbit Coupled Systems
• Intrinsic spin currents in ferromagnets
• Disentangling relativistic spin torques in a ferromagnet/semiconductor bilayer