Asymmetric Pt/Co/Pt structure as a platform for extracting pure spin Hall torque

TL;DR

This study demonstrates that asymmetric Pt/Co/Pt structures on GGG substrates serve as an effective platform for precise, temperature-independent measurement of pure spin Hall torque, eliminating Rashba effects through structural symmetry.

Contribution

It introduces a method to isolate and measure the pure spin Hall torque in Pt/Co/Pt trilayers, highlighting the importance of substrate choice and structural symmetry for accurate spin torque quantification.

Findings

Spin Hall torque is nearly temperature-independent from 10K to 300K.

Symmetric Pt/Co/Pt on GGG substrate effectively cancels Rashba torque.

Spin Hall angle of Pt remains constant across the studied temperature range.

Abstract

We have quantitatively studied the spin-orbit torque purely generated by the spin Hall effect in a wide range of temperatures by intensionally eliminating the Rashba spin-orbit torque using Pt/Co/Pt trilayers with asymmetric thicknesses of the top and bottom Pt layers. The vanishingly small contribution from the Rashba effect has been confirmed through the vector measurements of the current-induced effective fields. In order to precisely determine the value of the spin Hall torque, the complete cancelation of the spin Hall torque has been verified by fabricating symmetric Pt/Co/Pt structure on SiO2 and Gd3Ga5O12 (GGG) substrates. Despite of the complete cance- lation on the GGG substrate, the spin Hall torque cannot be completely canceled out even when the top and bottom Pt layers have same thicknesses on the SiO2 substrate, which suggests that Pt/Co/Pt trilayers on a GGG substrate is a suitable system for precise measurements of the spin Hall torque. The result of the vector measurements on Pt/Co/Pt/GGG from 300 to 10 K shows that the spin Hall torque is almost independent of temperature, which is quantitatively reproduced under the assumption of the temperature-independent spin Hall angle of Pt.