Fig. 3. Mechanism for 180° switching of the Néel vector by SOT.
(A) Schematic of n rotation driven by exchange torques Tex with p along +X and n along +Y. n can be simplified as (m1 − m2)/2 for cAFM Mn5Si3 with four sublattices where m1 = m3 and m2 = m4 (Materials and Methods). Damping-like SOT shares the same direction for m1 and m2 on opposite AFM sublattice as TDL ~ m1 × (p × m1) ~ m2 × (p × m2). Hence, TDL pulls m1 and m2 toward the direction of p, bringing about exchange torques Tex ~ m1 × Hex ~ m2 × Hex due to the AFM exchange field Hex, which alters on m1 and m2 to drive both m1 and m2 to rotate coherently. The rotation of n is accompanied by the motion of m, which is favorite by magnetic field H along +Y. (B) Schematic of energy barriers for the transition from n+ to n− and n− to n+. Without H, these two energy barriers are the same, determined by MAE. With nonzero H such as H > 0, the degeneracy between them cannot be maintained. (C) Simulated switching trajectories of m and n for positive p+ and positive H+ as well as (D) negative p− and positive H+. m is magnified 10 times for better visualization. The color of trajectories indicates the evolution time, where p is added from 0.05 ns to 0.15 ns.