Nodal‐Surface and Flat‐Band Driven Large Room‐Temperature Anomalous Nernst Effect in Epitaxial Ferromagnetic Weyl Metal Fe 5 Si 3

Magnetic topological materials exhibit unconventional transport arising from the interplay between exchange‐driven symmetry breaking and band topology. Beyond the point‐like singularities of Weyl and Dirac fermions, extended degeneracies such as nodal surfaces and flat bands constitute an emerging frontier whose impact on Berry‐curvature‐mediated transport remains largely unexplored. Here, the anomalous Nernst effect (ANE) is investigated in epitaxial thin films of the Weyl nodal‐line ferromagnet Fe 5 Si 3 . A pronounced transverse Nernst response of ∼1.50 µV K −1 is observed at room‐temperature, accompanied by a giant anomalous Nernst angle of ∼0.56, indicating highly efficient entropy‐to‐charge conversion. The ANE follows a robust − TlnT scaling over a wide temperature range, supporting its intrinsic Berry‐curvature origin. A substantial topological Nernst signal of ∼0.43 µV K −1 persisting above room‐temperature is consistent with a possible contribution from real‐space Berry‐curvature linked to nontrivial spin textures. First‐principles calculations and symmetry analysis reveal Weyl nodal lines, spin‐orbit coupling (SOC) gapped nodal surfaces, and nearly flat bands near the Fermi level. The close agreement between calculated and measured anomalous Nernst conductivity supports an intrinsic origin, with these features providing a plausible electronic framework for the strongly energy‐dependent Berry‐curvature. These results establish Fe 5 Si 3 as a low‐cost binary topological magnet for Berry‐curvature‐driven thermoelectric phenomena.