Temperature and magnetic field dependent grain boundary structures in skyrmion lattices via a quasiparticle-based mechanism

Skyrmion lattices, composed of densely packed ferromagnetic skyrmions, possess unique topological domain structures and can be tuned by external factors like force, magnetic fields, and temperature, making them promising for next-generation spintronic devices. Similar to atomic crystals, lattice defects, such as grain boundaries, exist within skyrmion lattices and are expected to have significant impact on the behaviors of skyrmion lattices. However, even the fundamental structures and external condition dependence of skyrmion grain boundaries remain poorly understood. In this study, we systematically investigated the skyrmion grain boundary structures and their dependence on external fields using phase-field simulations. Our results reveal that skyrmion grain boundaries are stabilized through skyrmion deformation, forming unique quasiparticle-based structures, while they consist of five to seven pair dislocations, analogous to those in conventional crystals. The degree of deformation strongly depends on both temperature and magnetic field: at low temperature and low magnetic field, skyrmions near the grain boundary undergo enhanced deformation, in order to reduce Dzyaloshinskii-Moriya interaction energy. Furthermore, our strain analysis shows that such local skyrmion deformations fundamentally alter the lattice mismatch relaxation mechanisms. These findings not only deepen the fundamental understanding of defect structures in topological magnetic systems but also provide insights relevant to the design of advanced spintronic devices.