First-principles calculations of spin-orbit torques in a Mn₂Au/HM bilayer

Mn₂Au is a collinear AFM and has a high Néel temperature above 1000 K. It has a tetragonal structure with a combination of inversion symmetry and time reversal symmetry which is also the symmetry of CuMnAs. This particular symmetry gives rise to opposite current-induced spin polarization on each sublattice when applying an electric field. The staggered spin polarization results in a non-staggered field-like (FL) spin-orbit torque (SOT), which is suitable for the switching of the AFM order.

In this work, by using first-principles calculations, we calculate the SOTs of a Mn₂Au/HM bilayer, where HM is W or Pt. By expanding the SOT using vector spherical harmonics, layer-resolved angular dependence of SOT is obtained. For FL SOT, it has a large contribution from the Mn₂Au and a small contribution from the HM. For DL SOT, it has most of the contribution from the HM. We found the SOT is sizable even 30 monolayers away from the interface, which indicates the spin current can penetrate very deeply in the AFM. FL SOT is non-staggered on each sublattice and it dominates the behavior of spin dynamics. DL SOT is staggered on each sublattice so that its net effect on spin dynamics is negligible. The effect of disorder strength on SOT is also studied.