Topological spin textures in centrosymmetric/van der Waals magnets

Topological swirling spin textures, such as skyrmions and merons, have recently attracted much attention as a unique building block for high-density magnetic information devices. Previous observations of skyrmions have mostly focused on noncentrosymmetric systems, where Dzyaloshinskii-Moriya interaction plays an important role. On the other hand, recent theoretical studies suggest that skyrmions can be stabilized even in centrosymmetric systems by considering different microscopic mechanisms. For example, geometrical frustration of short-range exchange interactions on triangular lattice is predicted to stabilize a hexagonal lattice of skyrmions. Another potential mechanism is the RKKY interactions mediated by itinerant electrons, which is expected to favor a skyrmion lattice state for highly-symmetric (such as hexagonal or tetragonal) crystal lattice systems.

In this talk, I overview the recent experimental discovery of skyrmions in centrosymmetric systems. In particular, we focus on the case of centrosymmetric tetragonal magnets, where the square lattice of skyrmions with extremely small diameter (1.9 nm for GdRu₂Si₂, i.e. the smallest value ever reported for single-component bulk materials[1]) has been observed. This class of materials (such as GdRu₂Ge₂[2] and EuAl₄[3]) often host multi-step toplotical transitions among a rich variety of skyrmion and meron crystal states, whose origin can be ascribed to the competition of RKKY interactions at inequivalent wave vectors. Non-coplanar topological spin texture has also been identified in a series of intercalated van der Waals magnets (CoTa₃S₆ and CoNb₃S₆)[4], and their nontrivial electron trasport properties are investigated.