Spin waves in ferro- and antiferromagnetic noncollinear magnets with Dzyaloshinskii-Moriya interaction

Broken inversion symmetry combined with the spin-orbit interaction generates a finite Dzyaloshinskii-Moriya interaction (DMI), which can induce noncollinear spin textures of chiral nature. In a ferromagnet, the DMI also causes the spin waves to be nonreciprocal, i.e., spin waves propagating with opposite wave vectors are characterized by different group velocities, energies, and lifetimes. We address the case of complex spin textures, such as ferro- and antiferromagnetic spin-spiral and skyrmion systems, where the manifestation of DMI-induced chiral asymmetries remains unexplored. We discuss such nonreciprocal effects and propose ways of accessing the magnitude and direction of the DMI vectors in the context of spin-polarized or spin-resolved inelastic scattering experiments. In particular, we show that even zero-net-magnetization systems, such as collinear antiferromagnets and cycloidal spin spirals, can have spin-wave modes that are individually nonreciprocal while the total spin-wave spectrum remains reciprocal.

Refs.: Phys. Rev. B 97 02443 (2018), Phys. Rev. B 102, 104401(2020), Phys. Rev. B 102, 104436(2020).