The electric-field induced spin-orbit torque (SOT) in antiferromagnetic (AFM) Weyl semimetals (WSMs) is theoretically investigated. Unlike in the ferromagnetic (FM) counterparts (1), the magnetic domain walls (DWs) in the AFM WSMs appears to lack the torsion in the magnetization and thus unable to benefit from this highly efficient mechanism that originates from the axial magnetic effect. Contrarily, our calculations illustrate that the addition of the Dzyaloshinskii-Morya interaction can introduce a twist in the magnetic moment, giving rise to the non-zero axial magnetic field and net spin current in the AFM textures subjected to an electric field. The non-zero components of the exchange fields of spin-polarized Weyl fermions are shown in Fig. 1. In the case of a Bloch DW (Fig. 1a), the direction of the driving field varies along the DW texture, significantly reducing the effect of SOT. Contrarily, the contribution of the unidirectional effective field along the Néel DW location (Fig. 1b) appears cumulative getting more efficiency. The dynamics of the DW motion is analyzed by considering the balance of energy absorption and dissipation. It reveals the need to account for the contribution of the exchange dissipation mechanism (2) beyond the Gilbert-like term to compensate the unusual superlinear rate of energy absorption by the AFM textures. The obtained DW velocity over the magnon velocity vm vs electric field shows a significant speed-up for the Néel DW in AFM WSMs (Fig.2) compared with the FM WSM as well as those in the non-topological FMs and AFMs. The results clearly indicate the significance of the axial magnetic effect in the dynamics of spin textures in AFM WSMs.
(1) D. Kurebayashi and K. Nomura, "Theory for spin torque in Weyl semimetal with magnetic texture," Sci. Rep. 9, 5365 (2019).
(2) J. H. Mentink, J. Hellsvik, D. V. Afanasiev, B. A. Ivanov, A. Kirilyuk, A. V. Kimel, O. Eriksson, M. I. Katsnelson, and Th. Rasing, "Ultrafast spin dynamics in multisublattice magnets," Phys. Rev. Lett. 108, 057202 (2012).