Néel-Vector-Dependent Unconventional Spin-Orbit Torque for Deterministic Field-Free Switching in NiO (110)-Based Trilayers.

Spin-orbit torque (SOT) provides an efficient route for ultrafast and energy-efficient magnetization control in spintronic devices. However, deterministic switching of perpendicular magnetization in conventional non-magnet/ferromagnet bilayers is fundamentally limited by symmetry, typically necessitating an external magnetic field. In this work, we demonstrate unconventional spin currents and associated SOTs in antiferromagnet (AFM)-based NiO(110)/Ta/CoFeB/MgO trilayers, enabling nearly complete field-free switching of perpendicular magnetization. We find that the switching efficiency is maximized when the applied current is oriented transverse to the AFM easy axis, indicating that the generated spin currents are governed by the relative orientation between the Néel vector and the current direction. Second-harmonic measurements reveal angle-dependent spin currents with both in-plane and out-of-plane spin polarizations, which is consistent with micromagnetic simulations incorporating the Néel-vector dynamics in the AFM layer. Our findings suggest that AFM-based trilayers offer a versatile platform for efficient field-free switching and highlight the potential of Néel-vector-dependent spin currents for SOT-based spintronic applications.