Noncollinear magnetic textures from quartic asymmetric exchange

Our work reveals a new potential source of noncollinear magnetic textures in certain classes of ferromagnets (FMs). Namely, in those that are described by the achiral tetrahedral symmetry (point group T_d) or by the trigonal prismatic symmetry (point group D_3h). The latter symmetry is realised in monolayer Fe₃GeTe₂, some transition metal dichalcogenides, and other two-dimensional FMs. It is known that the Dzyaloshinskii-Moriya interaction (DMI) does not contribute to the free energy density in such systems. We find all fourth order "chiral" contributions beyond DMI in T_d and D_3h classes. We study whether these "quartic asymmetric exchange" terms can explain spin spirals observed in a recent experiment on Fe₃GeTe₂. We also find that these asymmetric terms might stabilize bimerons — the in-plane analog of skyrmions. Finally, we estimate the radius of such bimerons analytically.

[1] I. A. Ado, G. Rakhmanova, D. A. Zezyulin, I. Iorsh, and M. Titov, arXiv:2105.14495 (2021)

[2] I. A. Ado, O. Tchernyshyov, and M. Titov, Phys. Rev. Lett. 127, 127204 (2021)