New mechanism for generating spin transfer torque without charge current

TL;DR

This paper introduces a novel physical mechanism to generate spin-transfer torque through electron interference effects, enabling magnetization switching without charge current by using an insulating barrier in a junction.

Contribution

It proposes a new out-of-plane spin-transfer torque mechanism based on electron interference, distinct from conventional charge-current-driven methods.

Findings

Out-of-plane torque $T_{ot}$ is proportional to bias and comparable to conventional torque.

Charge current and in-plane torque $T_{\ ext{\parallel}}$ are suppressed by the insulating barrier.

Potential for bias-induced magnetization switching without charge current.

Abstract

A new physical mechanism for generating spin-transfer torque is proposed. It is due to interference of bias driven nonequilibrium electrons incident on a switching junction with the electrons reflected from an insulating barrier inserted in the junction after the switching magnet. It is shown using the rigorous Keldysh formalism that this new out-of-plane torque $T_{\perp}$ is proportional to an applied bias and is as large as the torque in a conventional junction generated by a strong charge current. However, the charge current and the in-plane torque $T_{\parallel}$ are almost completely suppressed by the insulating barrier. This new junction thus offers the highly applicable possibility of bias-induced switching of magnetization without charge current.