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

TL;DR

This study measures the spin Hall angle in epitaxial Pt films, highlighting the influence of interface roughness and demonstrating that epitaxial growth can enhance spin-to-charge conversion efficiency.

Contribution

It provides a precise determination of the spin Hall angle and spin mixing conductance in epitaxial Pt, emphasizing the role of interface quality in spin pumping experiments.

Findings

Spin Hall angle of (5.7 ± 1.4)% in epitaxial Pt.

Spin diffusion length of 1.1 nm in epitaxial Pt.

Interface engineering can improve spin-to-charge conversion.

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.