Efficient conversion of orbital Hall current to spin current for spin-orbit torque switching

TL;DR

This paper demonstrates efficient methods to convert orbital Hall currents into spin currents via spin-orbit coupling engineering, significantly enhancing spin torque for magnetic switching in spintronic devices.

Contribution

It introduces two effective methods for orbital-to-spin current conversion, enabling unambiguous demonstration of orbital Hall torque and improving spin-orbit-torque device performance.

Findings

Orbital Hall torque is enhanced by Gd or Pt layers.

Orbital current in Cr is efficiently converted into spin current.

Reduction in switching current for perpendicular magnetization.

Abstract

Spin Hall effect, an electric generation of spin current, allows for efficient control of magnetization. Recent theory revealed that orbital Hall effect creates orbital current, which can be much larger than spin Hall-induced spin current. However, orbital current cannot directly exert a torque on a ferromagnet, requiring a conversion process from orbital current to spin current. Here, we report two effective methods of the conversion through spin-orbit coupling engineering, which allows us to unambiguously demonstrate orbital-current-induced spin torque, or orbital Hall torque. We find that orbital Hall torque is greatly enhanced by introducing either a rare-earth ferromagnet Gd or a Pt interfacial layer with strong spin-orbit coupling in Cr/ferromagnet structures, indicating that the orbital current generated in Cr is efficiently converted into spin current in the Gd or Pt layer. Furthermore, we show that the orbital Hall torque can facilitate the reduction of switching current of perpendicular magnetization in spin-orbit-torque-based spintronic devices.