Determination of the spin Hall angle in single-crystalline Pt films from spin pumping experiments

Abstract: We report on the determination of the spin Hall angle and the identification of the role of the interface roughness for the inverse spin Hall effect (ISHE) in ultra-clean, defect-reduced epitaxial Pt films. By applying vector network analyzer ferromagnetic resonance spectroscopy to a series of single crystalline Fe (12 nm) /Pt (t$_\text{Pt}$) bilayers we determine the real part of the spin mixing conductance $(4.4:\pm:0.2)\cdot 10^{19}: $m$^{-2}$ and reveal a very small spin diffusion length in the epitaxial Pt $(1.1:\pm:0.1)$ nm film. We investigate the spin pumping and ISHE in a stripe microstucture excited by a microwave coplanar waveguide (CPW) antenna. By using their different angular dependencies, we distinguish between spin rectification effects and the inverse spin Hall effect. The relatively large value of the spin Hall angle $(5.7 \pm 1.4): \% $ hints that interface engineering by epitaxially grown non-magnetic materials can increase the spin-to-charge current conversion efficiency.