Investigating microwave properties and modulating dampling parameter in NM/FM thin films for spintronics applications

Microwave properties were investigated in Ta/NiFe $N_{i 81} F_{e 19} \approx$. Permalloy, Py) bilayer system using electrically driven spin torque ferromagnetic resonance (STFMR) technique focusing particularly using frequency sweep measurements. Frequency sweep STFMR signals were detected via spin Hall effect of Ta. This technique was optimized for achieving high signal-to-noise (SNR) ratio and anisotropic magnetoresistance of 1.5% was achieved. The Gilbert damping constant can be tuned by applying an electric current which shows the evidence of spin torque in the system. The value of $\alpha$ is found to be $0.0085 \pm 0.0002$ at $I_{\mathrm{dc}}=0 \mathrm{mA}$. Further, $\theta_{\mathrm{SH}}=-0.160 \pm 0.027$, an important parameter describing performance of Ta was calculated and the parameters quantified corroborate with widely used field sweep technique discussed in literature. The interface transparency, $T=\sim 0.40$, is large which accounts for the flow of spin current density that diffuses into the Py layer via SHE of Ta. Further, these studies are beneficial for the development of Ta/Py based spin Hall nano-oscillators (SHNO) which can generate RF power by application of dc current.