Evaluation of spin mixing conductance in Co2FeGa0.5Ge0.5/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 (g_eff^(↑↓)) of (2.78±0.09)×1019 m-2 was evaluated. Further, to investigate the effect of interface property on g_eff^(↑↓), ultrathin (~ 0.2 nm) Cu, Ni, Ru, Ta, or Cr insertion layers were introduced between the Co2FeGa0.5Ge0.5 and Pt. Inserting a non-magnetic (NM) Cu layer results in a pronounced decrease of g_eff^(↑↓) g_eff^⇵, whereas the FM Ni layer leavesg_eff^(↑↓) g_eff^⇵ nearly unchanged. In the case of Ru and Ta insertion layers, a modest reduction in g_eff^(↑↓) g_eff^⇵ is observed despite their NM nature. The antiferromagnetic Cr insertion layer also causes a small decrease in g_eff^(↑↓) g_eff^⇵. The observed change in g_eff^(↑↓) depends on the insertion material, indicating that their physical properties, such as magnetic, non-magnetic, antiferromagnetic, light or heavy metal, reflect on g_eff^(↑↓).