Enhanced Spin-Orbit-Torque Efficiency inW−Co20Fe60B20Multilayers by Insertion of anIrxMn1−xorPtxMn1−xLayer

Abstract

Spin-orbit torque (SOT) has great potential application for developing next-generation magnetic random-access memory (MRAM). For efficient utilization of the SOT MRAM, most efforts have been focused on reducing power consumption by improving the SOT efficiency. Here, we report that inserting an ultrathin ${\mathrm{Ir}}_x{\mathrm{Mn}}_{1\text{−}x}$ (or ${\mathrm{Pt}}_x{\mathrm{Mn}}_{1\text{−}x}$) layer at the heavy-metal–ferromagnet interface is an effective strategy to increase the SOT efficiency. By performing spin-torque ferromagnetic magnetic resonance and second-harmonic Hall measurements, we found that the absolute values of the charge-to-spin conversion efficiency increase from 0.09 for annealed W-${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ (CFB) sample to 0.15 for annealed $\mathrm{W}\text{−}{\mathrm{Ir}}_x{\mathrm{Mn}}_{1\text{−}x}$-CFB sample. The enhancement of the SOT efficiency can be attributed to the reduction of interfacial spin-memory loss at the annealed $\mathrm{W}\text{−}{\mathrm{Ir}}_x{\mathrm{Mn}}_{1\text{−}x}$ (or ${\mathrm{Pt}}_x{\mathrm{Mn}}_{1\text{−}x})\text{−}\mathrm{CFB}$ samples. Moreover, current-driven magnetization switching with a reduced critical current density has been achieved in the annealed $\mathrm{W}\text{−}{\mathrm{Ir}}_x{\mathrm{Mn}}_{1\text{−}x}\text{−}\mathrm{CFB}$ samples. This study highlights the significant roles of the ${\mathrm{Ir}}_x{\mathrm{Mn}}_{1\text{−}x}$ (or ${\mathrm{Pt}}_x{\mathrm{Mn}}_{1\text{−}x}$) insertion layer on improving the SOT efficiency and provides a strategy to improve the SOT efficiency through nanoengineering of the ${\mathrm{Ir}}_x{\mathrm{Mn}}_{1\text{−}x}$ (or ${\mathrm{Pt}}_x{\mathrm{Mn}}_{1\text{−}x}$) insertion layer for energy-efficient SOT devices.