Berry phase contribution to the spin-orbit torque in an antiferromagnet with weak ferromagnetic order.

The previous theoretical [1] and experimental [2] antiferromagnet-generated spin-orbit torque studies are yet limited to ideal antiferromagnets where magnetization is strictly collinear so that anti-unitary symmetries, such as the combinations between time-reversal and spatial inversion or time-reversal and lattice translation, are preserved. Even in antiferromagnets with collinear spin configurations in equilibrium, however, spin configurations become noncollinear during their magnetization dynamics and the anti-unitary symmetries are broken [3]. In this talk, I show theoretically that the noncollinearity, which breaks anti-unitary symmetry, of antiferromagnet due to magnetization dynamics, can significantly modify properties of Berry phase contribution to the spin-orbit torque in clean antiferromagnets.

[1] J. Zelezný et al., Phys. Rev. Lett. 113, 157201 (2014); Phys. Rev. B 95, 014403 (2017).
[2] P. Wadley et al., Science 351, 587 (2016).
[3] A. C. Swaving et al., Phys. Rev. B 83, 054428 (2011).