Magnetization-Tunable Topological Phase Transitions in Ferromagnetic Kagome Monolayers of Co$_3$X$_3$Y$_2$ ($X=\mathrm{Sn},\mathrm{Pb}$; $Y=\mathrm{S},\mathrm{Se}$)

Abstract

The quantum anomalous Hall effect in magnetic kagome materials has emerged as a versatile platform for dissipationless electronic and spintronic devices. In this work, we demonstrate that the orientation of magnetic moments $\hat{m}(\theta,\phi)$ at lattice sites provides a practical tuning mechanism for engineering nontrivial topological phases in monolayer kagome ferromagnets. To elucidate the mechanism, 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 and can capture the resulting topological phase diagram as a function of $\hat{m}(\theta,\phi)$. In particular, the restoration of in-plane mirror symmetry for specific values of $\phi$ drives a topological phase transition upon varying the in-plane orientation of the moments $\hat{m}(\theta = 90^{\circ}, \phi)$. In contrast, for fixed $\phi$, the transitions driven by varying $\theta$ originate from the competition between Rashba SOC and intrinsic SOC. Density functional theory calculations for ferromagnetic kagome monolayers belonging to the Co$_3$X$_3$Y$_2$ family ($X=\mathrm{Sn},\mathrm{Pb}$; $Y=\mathrm{S},\mathrm{Se}$) support the predictions of the proposed minimal tight-binding model. These findings provide design guidelines for tunable topological phases in kagome materials.