Skyrmion–meron transformation via an intermediate multi-Q state in a bilayer chiral magnet

We investigate the evolution of topological spin textures in a bilayer chiral magnetic system with easy-plane anisotropy by means of Monte Carlo simulations. The magnetic configurations are analyzed using real-space spin snapshots, spin structure factors, and topological charge calculations in order to characterize the underlying magnetic phases. Our results show that increasing easy-plane anisotropy progressively destabilizes the skyrmion lattice and drives the system toward a meron–antimeron crystal configuration. Importantly, the transformation does not occur through a direct phase transition. Instead, an intermediate regime emerges in which the spin texture exhibits an intermediate multi-Q structure characterized by competing modulation vectors. This intermediate state is clearly identified in the structure-factor patterns and reflects the coexistence of different spin modulations in the system. Furthermore, spatial mappings of the local topological charge rigorously verify these phenomenological classifications by confirming the integer charge of skyrmions, the fractional nature of merons, and the macroscopic charge cancellation within the intermediate regime. At sufficiently strong magnetic fields, the system approaches a nearly field-polarized phase with residual chiral fluctuations. These findings provide insight into the mechanisms governing topological phase evolution in bilayer chiral magnets and highlight the role of magnetic anisotropy in controlling transitions between skyrmion and meron-based spin textures.