Band Structure Engineering to Optimize Spin‐Wave Propagation in Weyl ferromagnet Co₂MnGa1‐xGex

Spin waves, the quantized excitations of magnetic order, have been widely explored as low‐power information carriers in conventional metallic systems (e.g., NiFe) and insulating materials like yttrium iron garnet (YIG). Recently, magnetic Weyl semimetals (WSMs) have emerged as a novel platform for magnonics, leveraging their unique band structures, strong spin‐orbit interactions, and fertile topological behavior. Despite this potential, spin‐wave dynamics in magnetic WSMs remain largely uncharted. In this work, this gap is addressed by investigating spin‐wave propagation in epitaxial Co 2 MnGa 1‐ x Ge x (0 ≤ x ≤ 1) thin films, a prototypical magnetic WSMs system. By changing the ratio between Ga and Ge, how band‐structure engineering, specifically tuning the Fermi level into the minority‐spin pseudogap is demonstrated, systematically modulates the electronic and magnetic properties to achieve ultralow Gilbert damping (≈1.5 × 10 −3 ) alongside long spin‐wave decay lengths over 100 µm. These results establish a generalizable strategy for optimizing spin‐wave media while unlocking a materials platform to probe intertwined charge, spin and orbit, with profound implications for next‐generation spintronic and magnonic technologies.