Important role of magnetization precession angle measurement in inverse spin Hall effect induced by spin pumping

Abstract

Here, we investigate the spin Hall angle of Pt in a Ni80Fe20/Pt bilayer system by using a broadband spin pumping and inverse spin Hall effect measurement. An out-of-plane excitation geometry with an application of external magnetic field perpendicular to the charge current direction is utilized in order to suppress unwanted galvanomagnetic effects. Magnetization precession angle (θC) on ferromagnetic resonance for wide excitation frequency range (4–14 GHz) is estimated from the rectification voltage of anisotropic magnetoresistance (AMR) and a conventional method of using the microwave power in a coplanar waveguide. A marked difference in θC profiles for the different methods is observed, resulting in the large variation in estimated values of spin current density at Ni80Fe20/Pt interface. The frequency dependence of the spin current density estimated using the AMR effect is found to be similar to that of the inverse spin Hall voltage. We obtain the frequency-invariant spin Hall angle of 0.067 ± 0.002.