Strain-Induced Enhancement of Spin Pumping in Pt/YIG Bilayers

Abstract: Enhancing spin-to-charge (S$\rightarrow$C) conversion efficiency remains a key challenge in spintronic materials research. In this work we investigate the effect of substrate-induced strains onto the S$\rightarrow$C efficiency. On one hand, we analyze strains-induced magnetic anisotropies in yttrium iron garnet (Y$3$Fe$_5$O${12}$, YIG) by comparing the magnetic and structural properties of YIG films grown on Gd$3$Ga$_5$O${12}$ (GGG) and (CaGd)$3$(MgZrGa)$_5$O${12}$ (SGGG) substrates. Differences in lattice mismatch - YIG//GGG ($\eta = -0.06 \%$) and YIG//SGGG ($\eta = -0.83 \%$) - lead to out-of-plane tensile strains in the first case and unexpected compressive strain in the latter. On the other hand, we study the spin injection efficiency on Pt/YIG bilayers evaluated by the Inverse Spin Hall Effect (ISHE). We find that the resulting perpendicular magnetic anisotropy in YIG//SGGG, while not dominant over shape anisotropy, correlates with enhanced ISHE signals as observed in Spin Pumping Ferromagnetic Resonance (SP-FMR) and Spin Seebeck effect (SSE) experiments. Strain engineering proves effective in enhancing spin-to-charge conversion, providing insight into the design of efficient spintronic devices.