Ab initio amorphous spin Hamiltonian for the description of topological spin textures in FeGe

Abstract

Topological spin textures in magnetic materials such as skyrmions and hopfions are interesting manifestations of geometric structures in real materials, concurrently having potential applications as information carriers. In the crystalline systems, the formation of these topological spin textures is well understood as a result of the competition between interactions due to symmetry breaking and frustration. However, in systems without translation symmetry such as amorphous materials, a fundamental understanding of the driving mechanisms of non-trivial spin structures is lacking owing to the structural and interaction complexity in these systems. In this work, we use a suite of first-principles-based calculations to propose an ab initio spin Hamiltonian that accurately represents the diversity of structural and magnetic properties in the exemplar amorphous FeGe. Monte Carlo simulations of our amorphous Hamiltonian find emergent skyrmions that are driven by frustrated geometric and magnetic exchange, consistent with those observed in experiment. Moreover, we find that the diversity of local structural motifs results in a large range of exchange interactions, far beyond those found in crystalline materials. Finally, we observe the formation of large-scale emergent structures in amorphous materials, far beyond the relevant interaction length-scale in the systems, suggesting a new route to emergent correlated phases beyond the crystalline limit.