Band Structure Engineering to Optimize Spin-Wave Propagation in Weyl ferromagnet CoMnGa Ge.

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 CoMnGa Ge (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) 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.