Ultra-Stable Weyl Topology Driven by Magnetic Textures in the Shandite Compound Co3Sn2S(2-x)Sex

We employ state-of-the-art first-principles calculations to investigate the shandite compounds Co3Sn2S2, Co3Sn2SeS, and Co3Sn2Se2, which host Weyl fermions and complex magnetic textures. Their magnetic structures are governed primarily by exchange interactions and magnetocrystalline anisotropy, whereas the symmetry-allowed alternating-layer Dzyaloshinskii-Moriya interaction (DMI) is found to be negligible. We identify a previously unrecognized spin-chiral interaction (SCI) arising from the kagome lattice topology, which plays a decisive role in stabilizing the experimentally observed magnetic textures. The extracted magnetic parameters reproduce experimental trends, with the SCI emerging as a novel and dominant contribution. The calculated SCI strengths are 0.78 meV, 0.86 meV, and 0.87 meV for Co3Sn2S2, Co3Sn2SeS, and Co3Sn2Se2, respectively. Furthermore, we demonstrate that short-wavelength magnetic textures drive phase transitions of the Weyl nodes, resulting in band flattening and the opening of an emergent gap. This newly identified SCI, together with the associated electronically driven phase transitions, provides a promising route for manipulating transport properties in spintronic devices.