Deterministic Switching of the Néel Vector by Asymmetric Spin Torque

Abstract

Néel vector, the order parameter of collinear antiferromagnets, serves as a state variable in associated antiferromagnetic (AFM) spintronic devices to encode information. A deterministic switching of Néel vector is crucial for the write-in operation, which, however, remains a challenging problem in AFM spintronics. Here we demonstrate, based on analytical derivation and macro-spin simulations, that Néel vector switching can be generally achieved via a current-induced spin torque, provided the spin accumulations responsible for this torque are non-identical between opposite sublattices. This condition occurs widely in AFM films, as symmetry equivalence between sublattice-dependent spin accumulations is usually absent, allowing unequal spin accumulations induced by Edelstein effect or a spin current. Unlike previously studied spin torques induced by uniform or staggered spin accumulations -- where either the field-like or damping-like component dominates exclusively -- the asymmetric spin torque features cooperative contributions from both components, leading to Néel vector dynamics that are fundamentally distinct from previous expectations. Crucially, the static states stabilized by the asymmetric spin torque enable versatile Néel vector switching strategies -- field-free spin-transfer torque switching during current application, as well as field-free or field-assisted spin-orbit torque switching after the current pulse -- demonstrating that established spin torque techniques from ferromagnetic spintronics can be directly adapted to AFM systems, a capability absent in previous theoretical frameworks. Our work establishes a general mechanism for current-induced Néel vector switching, which is in principle feasible for all collinear antiferromagnets, and thus paves the route to realize efficient writing in AFM spintronics.