Quantifying Spin Hall Angles from Spin Pumping: Experiments and Theory

TLDR

Spin Hall effects intermix spin and charge currents even in nonmagnetic materials, potentially enabling spin transport without ferromagnets. The study demonstrates a method to quantify spin Hall effects by integrating Ni₈₀Fe₂₀|normal‑metal bilayers into a coplanar waveguide. A dc spin current is generated in the normal metal via spin pumping by ferromagnetic resonance; the transverse dc voltage along the bilayer is measured, and anisotropic magnetoresistance and spin Hall contributions are distinguished by symmetry using a developed theory. The authors quantitatively determine the spin Hall angles for Pt, Au, and Mo, and show that the method can be applied to any conductor, even those with very small spin Hall angles.

Abstract

Spin Hall effects intermix spin and charge currents even in nonmagnetic materials and, therefore, ultimately may allow the use of spin transport without the need for ferromagnets. We show how spin Hall effects can be quantified by integrating Ni{80}Fe{20}|normal metal (N) bilayers into a coplanar waveguide. A dc spin current in N can be generated by spin pumping in a controllable way by ferromagnetic resonance. The transverse dc voltage detected along the Ni{80}Fe{20}|N has contributions from both the anisotropic magnetoresistance and the spin Hall effect, which can be distinguished by their symmetries. We developed a theory that accounts for both. In this way, we determine the spin Hall angle quantitatively for Pt, Au, and Mo. This approach can readily be adapted to any conducting material with even very small spin Hall angles.