Computational discovery of ferromagnetic AT6X6 kagome compounds

We present a systematic high-throughput density-functional-theory investigation of the structural and magnetic stability of 312 substitutional compounds in the magnetic kagome AT6X6 family. Our screening confirms the stability of many previously reported structures and predicts several additional stable candidates. Within collinear spin configurations, we find that Fe-based systems predominantly adopt antiferromagnetic ground states, whereas Mn-based analogues exhibit a more balanced distribution between ferromagnetic and antiferromagnetic order. For compounds exhibiting several nearly degenerate collinear configurations, we analyze the nature of their magnetic ground states, assess the possible emergence of non-collinear order, and discuss the limitations and uncertainties inherent to standard density-functional approaches. Our electronic-structure analysis further reveals that newly predicted ferromagnetic kagome systems display characteristic features of topological metals, with rich magnetic configurations that can be tuned by chemical substitution. Overall, these ferromagnetic kagome compounds constitute a broad and still largely unexplored materials platform for the emergence of exciting magneto-transport phenomena.

💡 Research Summary

The authors present a high‑throughput density‑functional‑theory (HT‑DFT) study of the AT₆X₆ kagome family, where A is a spacer cation, T a transition metal occupying the kagome lattice, and X a p‑block element. By combinatorially substituting 12 A‑site elements (Li, Na, K, Rb, Sr, La, Ti, Hf, Nb, Mg, Sc, Y), two T‑site elements (Fe, Mn), and three X‑site elements (Ge, Sn, Ga), they generate 312 distinct compositions. Four experimentally known structural prototypes (type 1–4) are used as templates; all structures are fully relaxed with VASP using PAW‑PBE, a 520 eV plane‑wave cutoff, and a k‑point spacing of 2π × 0.033 Å⁻¹. Initial relaxations are performed in a ferromagnetic (FM) configuration, after which collinear magnetic energies are evaluated for FM and three antiferromagnetic stackings (AFM1, AFM2, AFM3) that preserve in‑plane FM order.

Thermodynamic stability is assessed via formation energies and distances to the convex hull, using reference phases from the Materials Project. Compounds with hull distances ≤30 meV/atom are classified as metastable, yielding 233 candidates. The screening reproduces all previously reported stable AT₆X₆ phases (e.g., MgFe₆Ge₆, ScFe₆Sn₆) and uncovers several new potentially synthesizable materials, such as NaFe₆Ge₆, LiMn₆Ge₆, NaMn₆Ge₆, LaMn₆Ge₆, TiMn₆Ge₆, and NbMn₆Ge₆.

Magnetic analysis shows a clear dichotomy: Fe‑based compounds overwhelmingly favor the AFM1 collinear state, with energy differences of 10–30 meV per transition‑metal atom relative to FM, consistent with experimental observations. Mn‑based systems display a more balanced competition between FM and AFM states; many have FM–AFM energy gaps below 5 meV/TM, indicating near‑degeneracy and a susceptibility to non‑collinear (NC) spin textures. The authors introduce a simple Heisenberg‑model based criterion: when the FM–AFM energy difference |ΔE| < 15 meV, the system is flagged as potentially NC. For the Ga‑based series, MgFe₆Ga₆ is predicted to be FM, while the other AFe₆Ga₆ compounds (A = Sc, Y, Zr, Hf) favor AFM2 with only a few meV separation from FM, suggesting that synthesis conditions could tip the balance.

Electronic‑structure calculations (including spin‑orbit coupling in a post‑processing step) reveal that the newly identified FM candidates retain the hallmark kagome band features: Dirac points, flat bands, and van Hove singularities near the Fermi level. SOC lifts degeneracies and generates Weyl points and sizable Berry curvature, which are the microscopic origin of large anomalous Hall and Nernst effects reported in related kagome magnets. Chemical substitution on the A and X sites allows fine‑tuning of the Fermi level, offering a route to engineer the interplay between topology, magnetism, and correlation.

The paper also discusses methodological limitations. The high‑throughput workflow assumes negligible magneto‑volume effects and relies on the semi‑local PBE functional, which can underestimate correlation and magnetic anisotropy. The authors suggest that more sophisticated treatments (e.g., DFT+U, hybrid functionals, DMFT) are needed for quantitative predictions of non‑collinear ground states and for accurate estimation of magnetic transition temperatures.

In summary, this work delivers a comprehensive computational map of structural, magnetic, and electronic properties across a broad compositional space of AT₆X₆ kagome compounds. It validates known trends, predicts several hitherto unknown stable ferromagnets, and highlights the prevalence of near‑degenerate magnetic states that could host exotic non‑collinear order and topological transport phenomena. The identified candidates provide clear experimental targets for synthesis, neutron diffraction, ARPES, and transport measurements, and they open a promising avenue toward designing tunable magnetic topological metals based on kagome lattices.