Giant anisotropy of Gilbert damping in a Rashba honeycomb antiferromagnet

TL;DR

This paper reveals a giant anisotropy in Gilbert damping caused by strong Rashba spin-orbit coupling in a 2D antiferromagnet, leading to ultrafast in-plane Nél vector precession and suppressed spin-flip processes.

Contribution

It demonstrates how Rashba spin-orbit coupling induces giant damping anisotropy and supports undamped dynamical modes in a 2D antiferromagnetic honeycomb lattice.

Findings

Giant damping anisotropy linked to Rashba spin-orbit coupling.

Suppression of certain spin-flip processes due to band splitting.

Existence of an undamped in-plane Nél vector precession mode.

Abstract

Giant Gilbert damping anisotropy is identified as a signature of strong Rashba spin-orbit coupling in a two-dimensional antiferromagnet on a honeycomb lattice. The phenomenon originates in spin-orbit induced splitting of conduction electron subbands that strongly suppresses certain spin-flip processes. As a result, the spin-orbit interaction is shown to support an undamped non-equilibrium dynamical mode that corresponds to an ultrafast in-plane N\'eel vector precession and a constant perpendicular-to-the-plane magnetization. The phenomenon is illustrated on the basis of a two dimensional $s$-$d$ like model. Spin-orbit torques and conductivity are also computed microscopically for this model. Unlike Gilbert damping these quantities are shown to reveal only a weak anisotropy that is limited to the semiconductor regime corresponding to the Fermi energy staying in a close vicinity of antiferromagnetic gap.