Role of Spin Transport on Ultrafast Spin Dynamics in Magnetic Weyl Semimetal (Co₂MnGa)/Pt Heterostructures with High Spin‐Mixing Conductance

Magnetic Weyl semimetals are emerging as a new class of material systems for spintronics due to their intrinsic topological properties and the inherent interplay between topology and magnetism, giving rise to novel electronic states and spin‐orbital‐related effects. Here, ultrafast magnetization dynamics in the Weyl semimetal Heusler ferromagnet Co 2 MnGa is investigated, from femtosecond to nanosecond timescales, using time‐resolved magneto‐optical Kerr effect (TR‐MOKE) at room temperature. Ultrafast demagnetization and precessional dynamics corresponding to the Kittel and perpendicular standing spin‐wave (PSSW) modes of Co 2 MnGa, interfaced with Pt thin films of varying thickness, have been investigated. The exchange stiffness constant of Co 2 MnGa is determined, as well as detailed information about spin‐transport across the Co 2 MnGa/Pt interface. From the modulation of Gilbert damping of Co 2 MnGa with Pt thickness, a very high intrinsic spin‐mixing conductance, G ↑↓ = 1.73 × 10 16 cm −2 is extracted of the interface and the spin diffusion length of Pt is determined to be 2.9 ± 0.2 nm. The interfacial spin transparency is found to reach a sizeable value of ≈83%, in the perfect spin‐sink regime, suggesting the great potential of this heterostructure for spin‐orbitronics and devices relying on ultrafast magnetization dynamics.