Microscopic Origin of Spin Transfer Torque and Tunneling Spin Currents in Non-collinear Antiferromagnets

Antiferromagnetic materials with non-collinear spin textures have emerged as promising platforms for spintronics due to their vanishing magnetization, ultrafast dynamics, and unique magnetic order. Of particular interest are antiferromagnetic tunnel junctions (AFMTJs) exhibiting a sizable tunneling magnetoresistance (TMR) effect, as predicted theoretically [1] and demonstrated experimentally [2]. In these systems, bond currents between different magnetic sublattices can carry spin polarization while the total charge current remains unpolarized, producing sublattice-dependent tunneling spin currents and site-dependent spin transfer torque (STT). Using first-principles density functional theory (DFT) calculations, we evaluate site-dependent STT in AFMTJs based on non-collinear Mn₃Pt with the Γ_4g magnetic order and tunneling along the [111] direction. A complementary tight-binding model is constructed to illustrate the microscopic origin of site-dependent STT, showing that it arises intrinsically from the non-collinear antiferromagnetic order. This combined approach highlights how non-collinear antiferromagnets, such as those with Γ_4g and Γ_5g magnetic orders can generate large, tunable spin torques suitable for controlling magnetic order in next-generation ultrafast, all-antiferromagnetic spintronic devices.

References

[1] G. Gurung, et al., Nat. Comm. 15, 10242 (2024).

[2] J. Kang, et al. arXiv preprint. arXiv:2509.03026 (2025).