Enhanced spin–orbit torques in strained NiFe/Pt bi-layers on flexible substrate

Magnetization manipulation caused by spin–orbit torque is one of the central themes investigated in spintronics domain. The spin–orbit torque efficiencies can be manoeuvred by application of mechanical strain. In this direction, this study furthers the effort in understanding the evolution of spin–orbit torque efficiencies in mechanically strained ferromagnet (FM)/heavy metal(HM) (Ni81Fe19/Pt) bi-layer films on flexible kapton substrate, by the use of spin torque ferromagnetic resonance (ST-FMR) measurement technique. We report a tensile strain induced enhancement in damping-like and field-like spin–orbit torque efficiencies. The effective damping-like spin torque conductivity increased by 42% on the application of 0.312% tensile strain, which is encouraging from the magnetization switching application point of view. In order to investigate the driving factors behind the enhanced damping-like spin torque conductivity, ab-initio calculations were also carried out. Our findings provide insights into the workings of strain in FM/HM bi-layer stack and is a step forward in the implementation of flexible spintronics devices.