Origin of unexpected weak Gilbert damping in the LSMO/Pt bilayer system

Abstract: We present a first-principles and semiclassical analysis of the puzzling observation that a La${0.7}$Sr${0.3}$MnO$_3$ (LSMO) thin film exhibits larger Gilbert damping than an LSMO/Pt bilayer, contrary to conventional spin-pumping expectations. Density-functional theory with Wannier interpolation yields an intrinsic damping for LSMO, which is smaller than that of LSMO/Pt, indicating that the observed high damping in LSMO must be extrinsic. Motivated by the self-induced inverse spin Hall effect (ISHE) reported by Gupta et al [Phys. Rev. B 109, 014437 (2024)], we show that LSMO's large spin Hall angle (~0.093) and low longitudinal conductivity facilitate efficient spin-to-charge conversion, enhancing damping. In contrast, Pt capping in LSMO/Pt increases longitudinal conductivity and suppresses interfacial spin Hall angle to 0.007, reducing spin-pumping-induced damping. A Valet-Fert analysis of the spin accumulation yields the spin-diffusion length in Pt and a finite anti-damping spin-orbit torque coefficient. Our findings reconcile the anomalous damping hierarchy and offer design rules for low-loss manganite heterostructures.