Dual mode spin to charge conversion using inverse spin Hall effect in NiFe/FeMn/NiFe multilayer thin films

Abstract

Microwave devices with more than one operating frequency and their ease of tunability are of great importance for high-frequency information processing. Magnetic thin films offer an unparalleled advantage of engineering different microwave bands that can be precisely tailored and reconfigured externally. Here, novel trilayer structures consisting of NiFe/FeMn/NiFe with varying anti-ferromagnetic FeMn layer thickness have been investigated by exploring their ferromagnetic resonance (FMR) properties and inverse spin Hall effect (ISHE) responses. Two-step magnetic hysteresis loops are observed for higher FeMn thickness (t ≥ 12 nm), where the bottom NiFe layer shows a comparatively more significant shift due to the presence of strong interfacial exchange coupling. FMR study reveales two resonant modes associated with the two ferromagnetic layers, which are distinguishable for higher thicknesses of FeMn or at high excitation frequencies. The choice of FeMn thickness determines the operating frequencies, which can be finely tailored by optimizing the FeMn thickness. Gilbert damping parameter is found to be in the range of 0.009 - 0.012 where the presence of exchange bias adds to the the scattering mechanisms. Prominent ISHE responses are obtained from the bottom NiFe layer as compared to the top NiFe layer. Variation of FeMn thickness also shows a strong influence on the spin pumping (Vsp), and perpendicular anisotropic magnetoresistance (VAMR⊥) components. The results are correlated with the efficiency of spin flow and spin-to-charge conversion of the FeMn layer. Our systems can be used as an emerging alternative for microwave detectors and microwave energy harvesters.