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

TL;DR

This study measures the spin Hall angle in Ni80Fe20/Pt bilayers using broadband spin pumping and inverse spin Hall effect, emphasizing the importance of accurately determining magnetization precession angles to obtain consistent results.

Contribution

It introduces a method to accurately measure magnetization precession angles and demonstrates its impact on estimating the spin Hall angle in ferromagnet/metal bilayers.

Findings

Spin Hall angle of 0.067 was determined.

Precession angle measurement methods significantly affect spin current estimates.

Frequency dependence of spin current density aligns with inverse spin Hall voltage.

Abstract

Here, we investigate spin Hall angle of Pt in Ni80Fe20/Pt bilayer system by using a broadband spin pumping and inverse spin Hall effect measurement. An out-of-plane excitation geometry with application of external magnetic field perpendicular to the charge current direction is utilized in order to suppress unwanted galvanomagnetic effects. Magnetization precession angle 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 microwave power in a coplanar waveguide. A marked difference in the precession angle 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 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.