Inverse Spin Hall Effect in NiFe / Normal Metal Bilayers

TL;DR

This study investigates the inverse spin Hall effect in NiFe/normal metal bilayers, highlighting the conditions needed for accurate spin Hall angle measurements and providing specific values for Py/Pt and Py/Au systems.

Contribution

It offers a comprehensive analysis of inverse spin Hall effect and anisotropic magnetoresistance in NiFe/metal bilayers, clarifying measurement conditions and quantifying spin Hall angles.

Findings

Spin Hall angles of 0.09 for Py/Pt and 0.008 for Py/Au.

Measurement conditions critically affect spin Hall angle quantification.

Temperature dependence of inverse spin Hall voltages in Py/Pt aligns with theoretical models.

Abstract

Spin pumping in ferromagnets provides a source of pure spin currents. Via the inverse spin Hall effect a spin current is converted into a charge current and a corresponding detectable DC-voltage. The ratio of injected spin current to resulting charge current is given by the spin Hall angle. However, the number of experiments more or less equals the number of different values for spin Hall angles, even for the most studied normal metal platinum. This publication provides a full study of inverse spin Hall effect and anisotropic magnetoresistance for different NiFe(Py) / normal metal bilayers using a coplanar waveguide structure. Angle and frequency dependent measurements strongly suggest that spin pumping and inverse spin Hall effect can be used to quantify spin Hall angles only if certain conditions are met. Ruling out the anisotropic magnetoresistance as a parasitic voltage generating effect measurements of the inverse spin Hall effect in Py/Pt and Py/Au yield spin Hall angles of 0.09 and 0.008 respectively. Furthermore, DC-voltages at ferromagnetic resonance for Py/Pt are studied as a function of temperature and the results are compared to theoretical models.