Evaluation of spin mixing conductance in Co 2 Fe Ga 0.5 Ge 0.5 / Pt bilayer and the effect of ultrathin Cu, Ni, Ru, Ta, or Cr insertion layers

Improving the spin mixing conductance at the ferromagnet/heavy metal (FM/HM) interface with a low Gilbert damping constant in the FM layer is a key requirement for developing efficient spintronic devices. To evaluate the potential of Co₂FeGa0.5Ge0.5 as the FM layers in such structures, epitaxial Co₂FeGa0.5Ge0.5 single-layer and Co₂FeGa0.5Ge0.5/Pt bilayer films were deposited on MgO substrates using magnetron sputtering, and their Gilbert damping constants were evaluated from ferromagnetic resonance spectra. While the single-layer samples exhibit a low damping constant of ~1.07×10^-3, an enhancement in the damping constant was observed in the bilayer samples due to spin pumping across the Co₂FeGa0.5Ge0.5/Pt interface, from which relatively large spin mixing conductance (geff^↑↓) of (2.78±0.09)×10¹⁹0.16em0exm^-2 was evaluated. Further, to investigate the effect of interface property on geff^↑↓, ultrathin (~0.2 nm) Cu, Ni, Ru, Ta, or Cr insertion layers were introduced between the Co₂FeGa0.5Ge0.5 and Pt. Inserting a nonmagnetic (NM) Cu layer results in a pronounced decrease of geff^↑↓, whereas the FM Ni layer leaves geff^↑↓ nearly unchanged. In the case of Ru and Ta insertion layers, a modest reduction in geff^↑↓ is observed despite their NM nature. The antiferromagnetic Cr insertion layer also causes a small decrease in geff^↑↓. The observed change in geff^↑↓ depends on the insertion material, indicating that their physical properties, such as magnetic, nonmagnetic, antiferromagnetic, light or heavy metal, reflect on geff^↑↓.