Detection of long-range orbital-Hall torques

TL;DR

This paper demonstrates a significant orbital-Hall torque in Nb and Ru bilayers, revealing long-range orbital transport effects distinct from traditional spin Hall phenomena, with implications for spintronics.

Contribution

It introduces the detection and quantification of long-range orbital-Hall torques in Nb and Ru, highlighting their unique thickness dependence and long-range nature.

Findings

Orbital-Hall torque is large and measurable in Nb and Ru bilayers.

Long-range orbital transport differs from conventional spin absorption.

Sign reversal and enhancement of damping-like torques observed.

Abstract

We report and quantify a large orbital-Hall torque generated by Nb and Ru, which we identify from a strong dependence of torques on the ferromagnets. This is manifested as a sign reversal and strong enhancement in the damping-like torques measured in Nb (or Ru)/Ni bilayers as compared to Nb (or Ru)/FeCoB bilayers. The long-range nature of orbital transport in the ferromagnet is revealed by the thickness dependences of Ni in Nb (or Ru)/Ni bilayers which are markedly different from the regular spin absorption in the ferromagnet that takes place within a few angstroms and thus it uniquely distinguishes the orbital Hall torque from the spin Hall torque.