Topological Phase Transitions in Kagome Ferromagnets: The Role of Intrinsic Rashba Spin-Orbit Coupling

The theoretically predicted Chern insulators have highlighted the potential of easy-axis kagome ferromagnets to host the quantum anomalous Hall effect. Similar topological phases may also arise from in-plane ferromagnetism through the breaking of certain mirror symmetries in kagome materials. In this work, we show that the interplay between magnetism and mirror symmetries makes ferromagnetic kagome systems a versatile platform for realizing nontrivial topological phases, with the orientation of magnetic moments m̂(θ, ϕ) at lattice sites serving as a key tuning parameter. We construct a symmetry-adapted minimal tight-binding model for kagome ferromagnets that includes intrinsic spin-orbit coupling (SOC) and the intrinsic Rashba SOC permitted by broken out-of-plane mirror symmetry between nearest-neighbor kagome sites, enabling us to capture the resulting topological phase diagram as a function of m̂(θ,ϕ). In particular, the restoration of in-plane mirror symmetry for specific values of ϕ drives a topological phase transition upon varying the in-plane orientation of the moments m̂(θ = 90◦ , ϕ). In contrast, for fixed ϕ, the transitions driven by varying θ originate from the competition between Rashba SOC and intrinsic SOC. Density functional theory calculations for the ferromagnetic kagome monolayer Co3Pb3S2, a representative compound belonging to the family Co3X3Y2(X = Sn, Pb; Y = S, Se), corroborate our predictions based on the proposed minimal tight-binding model.