Sub-20 nm spin textures with arbitrary topological charge stabilized by higher-order interactions

Abstract

Topological magnetization textures play a central role in modern magnetism. For many applications, spin textures with different topological charges $Q$ in the same system are particularly attractive. Although the coexistence of skyrmions and antiskyrmions ($|Q| = 1$) has been reported in inversion-symmetric magnets, extending this to high-$Q$ ($|Q| > 1$) textures with arbitrary charge remains elusive. Here, using an atomistic spin model parameterized from first-principles calculations, we predict the emergence of sub-20 nm high-$Q$ textures in Janus monolayers, van der Waals magnets of growing interest. We explore skyrmion and antiskyrmion rings as well as skyrmion bags with $|Q|$ up to 5, and characterize their nucleation mechanisms, thermal stability, and collapse pathways. We find that higher-order spin interactions (HOI), which extend the conventional bilinear-exchange Hamiltonian, are essential for stabilizing these high-$Q$ spin textures. The rings remain thermally stable at zero magnetic field. HOI substantially enhance their energy barriers while leaving their size nearly unchanged and stabilize them even in the absence of Dzyaloshinskii-Moriya interaction. Skyrmion bags, in contrast, nucleate only in the presence of HOI. In particular, the four-spin three-site interaction is the key ingredient preventing high-$Q$ textures from collapsing into the ferromagnetic state. Finally, we identify previously unreported parity-dependent collapse mechanisms for high-$Q$ textures. Our results establish HOI as an overlooked mechanism for high-$Q$ nucleation.