In-Plane Field-Direction Control of Multiple-Q States and Skyrmion Crystals in a Triangular-Lattice Magnet with \(D_{\textrm{3d}}\) Anisotropy

Abstract

We investigate multiple-Q magnetic states in a triangular-lattice spin model with a \(D_{\textrm{3d}}\)-type anisotropic interaction under in-plane magnetic fields. Focusing on the interplay between anisotropy and field orientation, we examine how the magnetic phases evolve when the field is applied along two inequivalent in-plane directions. By means of simulated annealing, we identify a wide variety of field-induced phases, including both topological and non-topological multiple-Q states. In the strong-anisotropy regime, the skyrmion crystal with a higher topological number of two, stabilized at zero field, is transformed into the conventional skyrmion crystal with a topological number of one under increasing magnetic field. This transition occurs without a change in the principal ordering wave vectors, indicating that a subtle reorganization of the triple-Q components governs the change in topology. In contrast, in the weak-anisotropy regime, the magnetic behavior is sensitive to the direction of the applied magnetic field. The system eventually selects a single-Q state for the x-directional magnetic field, while it continues to reside within the multiple-Q states, exhibiting several distinct triple-Q states characterized by different intensity distributions among the symmetry-related ordering wave vectors for the y-directional magnetic field. These results demonstrate that the direction of an in-plane magnetic field plays an active role in selecting competing magnetic states, not only modifying phase boundaries but also controlling the topology and internal structure of the spin textures. Our findings highlight a route to manipulate multiple-Q states in centrosymmetric magnets through the combined effect of anisotropic interactions and field orientation.