Enhanced spin–orbit torque efficiency and neuron-like behaviors in ferrimagnet/heavy-metal heterostructure

Abstract

Compensated ferrimagnetic materials such as Co–Tb and Co–Gd have been confirmed to have significant spin–orbit torque (SOT) efficiency. However, the large coercivity and a relatively small spin-mixing conductance may hinder the applications of the near compensated ferrimagnets. In this work, we investigate the SOT effect and its potential applications in Ta/Co–Tb/Pt heterostructures. Based on a Co-rich ferrimagnetic alloy, we obtain a significant SOT switching efficiency of 15 ± 1 (10−6 Oe cm2/A) and a considerable effective spin Hall angle of θeff=0.270 ± 0.005. Using harmonic Hall measurement, the temperature dependence of the damping-like effective field has been extracted. The SOT efficiency scales linearly with 1/Ms in the high-temperature range but significantly deviates from this linear scaling law at a lower temperature, which is near the compensation point. In the Tb rich Ta/Co–Tb/Pt SOT device, we demonstrate the functionality of a neuron and the dependence of firing possibility on the intensity of coming stimulus, which is mimicked by the SOT switching dynamics in the ferrimagnetic Co–Tb alloy.