Giant spin–orbit torques in W/MgO nanostructures for energy-efficient SOT-MRAM applications

Abstract

High critical switching current density (Jc) and limited charge-to-spin conversion efficiency [spin–orbit torque (SOT) efficiency, ξSOT] of heavy metal-based SOT channels are the two key challenges for the development of energy-efficient SOT magnetic random-access memory (SOT-MRAM). In this paper, we demonstrate a significant enhancement of SOT efficiency in β-tungsten (W) films through magnesium oxide (MgO) doping, achieved via co-sputtering (CS) and multilayer-heterostructure (MLH) deposition, respectively. The W/MgO nanostructures retain the β-phase and exhibit a remarkable increase in ξSOT, from 0.20 in pure W to 0.48 for CS films (4% MgO doping)—and even more impressively—to 0.51 for the MLH method. The drastic SOT efficiency improvement is attributed primarily to the significantly enhanced skew scattering induced by MgO incorporation. As direct performance gauges, Jc of W/MgO nanostructures is reduced by up to 50.6%, and the power consumption is lowered by over 42%, compared to pure W-based devices. These findings highlight W/MgO nanostructures as highly promising SOT channel materials for energy-efficient SOT-MRAM applications.