Harnessing Orbital Hall Effect in Spin-Orbit Torque MRAM

TL;DR

This paper demonstrates that integrating Ru layers with [Co/Ni]$_3$ ferromagnets enhances orbital Hall effect-driven spin-orbit torque efficiency, significantly reducing switching current and power in SOT-MRAM devices, thus advancing next-generation memory technology.

Contribution

The study experimentally validates the use of Ru layers to enhance orbital Hall conductivity and torque efficiency in SOT-MRAM, outperforming traditional Pt layers.

Findings

30% increase in damping-like torque efficiency with Ru layers

20% reduction in switching current using Ru compared to Pt

Over 60% reduction in switching power in Ru-based devices

Abstract

Spin-Orbit Torque (SOT) Magnetic Random-Access Memory (MRAM) devices offer improved power efficiency, nonvolatility, and performance compared to static RAM, making them ideal, for instance, for cache memory applications. Efficient magnetization switching, long data retention, and high-density integration in SOT MRAM require ferromagnets (FM) with perpendicular magnetic anisotropy (PMA) combined with large torques enhanced by Orbital Hall Effect (OHE). We have engineered PMA [Co/Ni]$_3$ FM on selected OHE layers (Ru, Nb, Cr) and investigated the potential of theoretically predicted larger orbital Hall conductivity (OHC) to quantify the torque and switching current in OHE/[Co/Ni]$_3$ stacks. Our results demonstrate a $\sim$30\% enhancement in damping-like torque efficiency with a positive sign for the Ru OHE layer compared to a pure Pt, accompanied by a $\sim$20\% reduction in switching current for Ru compared to pure Pt across more than 250 devices, leading to more than a 60\% reduction in switching power. These findings validate the application of Ru in devices relevant to industrial contexts, supporting theoretical predictions regarding its superior OHC. This investigation highlights the potential of enhanced orbital torques to improve the performance of orbital-assisted SOT-MRAM, paving the way for next-generation memory technology.