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

Dang Khoa Le, Eklavya Thareja, Bektur Konushbaev, Gina Pantano, Tom Saunderson, Manh-Huong Phan, Yuriy Mokrousov, Jacob Gayles

TL;DR

The paper investigates Co3Sn2S(2-x)Sex shandite compounds as magnetic Weyl semimetals where Weyl node topology can be manipulated by magnetic textures. Using first-principles FLAPW calculations, the authors identify a spin-chiral interaction (SCI) arising from the kagome lattice that dominates over the symmetry-allowed Dzyaloshinskii-Moriya interaction, with SCI strengths of 0.78, 0.86, and 0.87 meV for x = 0, 1, 2, respectively. They quantify exchange stiffness and magnetocrystalline anisotropy, showing perpendicular MCA and a Se-induced enhancement of MCA, alongside Curie temperatures that trend with Se content in agreement with experiments. The study demonstrates that short-wavelength spin textures drive Weyl-node phase transitions, evolving from Type-I to Type-II and eventually to a gapped state along selected propagation directions, with the Weyl topology in the x = 1 (inversion-asymmetric) case displaying notable robustness. These findings highlight SCI as a dominant mechanism for stabilizing complex magnetic textures and for tuning Berry-curvature–driven transport in spintronic devices, offering a path to controllable topological electronic states in kagome-based magnets.

Abstract

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.

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

TL;DR

The paper investigates Co3Sn2S(2-x)Sex shandite compounds as magnetic Weyl semimetals where Weyl node topology can be manipulated by magnetic textures. Using first-principles FLAPW calculations, the authors identify a spin-chiral interaction (SCI) arising from the kagome lattice that dominates over the symmetry-allowed Dzyaloshinskii-Moriya interaction, with SCI strengths of 0.78, 0.86, and 0.87 meV for x = 0, 1, 2, respectively. They quantify exchange stiffness and magnetocrystalline anisotropy, showing perpendicular MCA and a Se-induced enhancement of MCA, alongside Curie temperatures that trend with Se content in agreement with experiments. The study demonstrates that short-wavelength spin textures drive Weyl-node phase transitions, evolving from Type-I to Type-II and eventually to a gapped state along selected propagation directions, with the Weyl topology in the x = 1 (inversion-asymmetric) case displaying notable robustness. These findings highlight SCI as a dominant mechanism for stabilizing complex magnetic textures and for tuning Berry-curvature–driven transport in spintronic devices, offering a path to controllable topological electronic states in kagome-based magnets.

Abstract

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.
Paper Structure (1 section, 4 equations, 4 figures, 1 table)

This paper contains 1 section, 4 equations, 4 figures, 1 table.

Table of Contents

  1. Acknowledgements

Figures (4)

  • Figure 1: (a) Side view of lattice structure of Co$_3$Sn$_2$S$_{(2-x)}$Se$_x$, where Co, Sn, S, and Se atoms are indicated in blue, gray, yellow, and green, respectively. (b) The kagome lattice formed by the Co atoms shows the noncoplanar magnetic state with a nonzero scalar chiral product. The inset displays the magnetic directions of the Co$_1$, Co$_2$, and Co$_3$ atoms in the Cartesian coordinate system, labeled with red, blue, and green arrows, respectively. (c) The energy dispersion relation of all shandite compounds with the noncoplanar spin orientations. (d--f) The comparison of spin-orbit-induced energy in (d) Co$_3$Sn$_2$S$_2$, (e) Co$_3$Sn$_2$SeS, and (f) Co$_3$Sn$_2$Se$_2$ between the DFT calculations (circles) and the spin-orbit contribution terms (lines), where the antisymmetric exchange (DMI) is shown as a green dash--dot line, while the spin-chiral interaction (SCI) is shown as a blue dashed line.
  • Figure 2: The dispersion relation in flat spin spirals and magnetocrystalline anisotropy surface of all shandite compounds. (a-c) Energy dispersion of spin spirals along [1,0,0] [1,1,0] and [1,1,1] directions (without SOC consideration), for (a) Co$_3$Sn$_2$S$_2$, (b) Co$_3$Sn$_2$SeS, and (c) Co$_3$Sn$_2$Se$_2$. (d-f) Three-dimensional magnetocrystalline anisotropy surfaces reflect the magnetocrystalline anisotropy energy of (d) Co$_3$Sn$_2$S$_2$, (e) Co$_3$Sn$_2$SeS, and (f) Co$_3$Sn$_2$Se$_2$.
  • Figure 3: Electronic band structures and density of states (DOS) of Co$_3$Sn$_2$S$_2$ with different homogeneous spin spiral angles $\phi$. Band structure and DOS are illustrated for $\phi=0 ^{\circ}$ in (a-b), $\phi=72^{\circ}$ in (c-d), and $\phi=108^{\circ}$ in (e-f), respectively. The spin projection in DOS is along the x-direction.
  • Figure 4: Topological phase transitions of Co$_3$Sn$_2$S$_{2-x}$Se$_x$ are revealed, where Co$_3$Sn$_2$S$_2$, Co$_3$Sn$_2$SeS, and Co$_3$Sn$_2$Se$_2$ are in red, blue and green lines, respectively. (a-b) Distance between two Weyl crossings is plotted as a function of the spin spiral angle $\phi$ (along the direction q = [1, 0, 0]) and the noncoplanar angle $\theta$. (c-d) Position of the Weyl pairs according to the Fermi energy as a function of both the mentioned angles.