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

Sascha Keller,Evangelos Th Papaioannou,Matthias R Schweizer,Philipp Pirro,Andres Conca,Philipp Lang,Burkard Hillebrands,Dimitrios Karfaridis,Thomas Brächer,Björn Heinz,Thomas Kehagias,Thomas Meyer,Moritz Geilen,George Vourlias,Laura Mihalceanu

doi:10.1088/1367-2630/aabc46

Abstract

We report on the determination of the spin Hall angle 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 (tPt) bilayers we determine the real part of the spin mixing conductance (4.4 ± 0.2) × 1019 m−2 and reveal a very small spin diffusion length in the epitaxial Pt (1.1 ± 0.1) nm film. We investigate the spin pumping and ISHE in a stripe microstucture excited by a microwave coplanar waveguide 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 ± 1.4)% shows that ultra-clean e-beam evaporated non-magnetic materials can also have a comparable spin-to-charge current conversion efficiency as sputtered high resistivity layers.

Highlights

When a metallic ferromagnet is used, spin rectification (SR) effects, in particular anisotropic magnetoresistance and anomalous Hall effect, generate a DC voltage in the FM material at FMR
In a prior publication[21], we optimized the growth of epitaxial Fe/Pt bilayers for spin pumping experiments: We have shown that the real part of the spin mixing conductance g↑↓ and the inverse spin Hall efficiency could be increased by increasing annealing temperature from room temperature to 300◦C
We focus on the growth of the Fe/Pt bilayers, via X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) imaging and selected area electron diffraction (SAED) analysis, and explain the microstructuring process and design

Summary

INTRODUCTION

When a metallic ferromagnet is used, spin rectification (SR) effects, in particular anisotropic magnetoresistance and anomalous Hall effect, generate a DC voltage in the FM material at FMR. We have previously shown that this MgO capping layer has no influence on the Gilbert damping parameter α in ferromagnetic resonance spectroscopy measurements[3]. How the atomic roughness of the Fe/Pt interface influences the ISHE in epitaxial Pt. The HRTEM imaging along with SAED analysis (Fig. 2b) showed the perfect epitaxial growth relation of the bilayer on the MgO. The microstructuring process did not change the spin pumping properties, since we performed vector network analyzer ferromagnetic resonance spectroscopy (VNA-FMR) measurements with the sample before and after the process. They showed that the lineshapes and the Gilbert damping did not change.

VNA-FMR MEASUREMENTS

CALCULATION OF THE SPIN HALL ANGLE

Findings

CONCLUSIONS