Dual Mode Spin-to-Charge Conversion in Ta/NiFe/Ta/CoFeB/Ta Multilayer Thin Films With Varying Spacer Layer Thickness

The generation of multimode ferromagnetic resonance (FMR) in a single device and its conversion to a voltage signal is a cornerstone for the efficient engineering of spintronics devices. In this study, we systematically investigated the effect of spacer layer thickness on engineering the dual resonance modes and spin-to-charge conversion (SCC) efficiency in Ta/NiFe/Ta(t)/CoFeB/Ta multilayer thin films. We observed a two-step magnetic hysteresis loop behavior associated with two magnetic layers. The extent of this step in hysteresis is strongly sensitive to the variation of spacer layer thickness. Spacer layer thickness played a crucial role in the coupling strength of the two ferromagnetic (FM) layers. Consequently, our FMR study revealed dual resonance modes where the separation between the modes is strongly dependent on the interlayer coupling strength. The lowest damping was observed as 0.006 (0.007) associated with the NiFe(CoFeB) layer for the Ta/NiFe/Ta(12)/CoFeB/Ta sample. The SCC measurements were carried out using the inverse spin Hall effect (ISHE) experiment. A detailed angular study was performed to extract the various contributions of spin rectification and spin pumping components. The spin pumping contribution was found to be prominent for all the samples, indicating an efficient SCC. A significant voltage drop was observed due to the NiFe layer compared to the CoFeB layer for all the samples. This comprehensive report offers a novel avenue for multiple SCCs in a single device associated with its customizable dual-mode FMR based on engineering different interfaces.