Modeling Bond-Dependent Kitaev-like interaction in 2D Edge-Sharing Tetrahedral Magnets: FeX (X=Te, Se)

Abstract

Bond-dependent magnetic interactions, exemplified by the Kitaev model, are known to arise from the interplay between spin-orbit coupling(SOC) and specific coordination geometries, yet their existence has so far been predominantly associated with edge-sharing octahedral systems. Whether analogous interactions survive in edge- sharing tetrahedral environments - relevant to iron-based superconductor parent compounds - remains an open question. Here, we construct a Kitaev-like model for monolayer FeTe and FeSe and demonstrate the presence of a previously unrecognized bond-dependent Ising-type interaction, induced jointly by chalcogen-mediated SOC and the tetrahedral crystal-field geometry. By mapping the first-principles calculations derived magnetic anisotropy energy mapping across representative linear magnetic orders, we disentangle the bond-dependent contributions from single-ion anisotropy. We reveal that the Kitaev-like interaction dominates the magnetic anisotropy in FeTe, whereas in FeSe, it fiercely competes with a single-ion anisotropy of opposite sign. The resulting noncollinear local anisotropy axes generate intrinsic single-site spin frustration, providing a microscopic mechanism for magnetic disorder beyond isotropic exchange models. Our results establish edge-sharing tetrahedral magnets as a new setting for bond-dependent interactions and extend the scope of Kitaev physics beyond octahedral coordination.