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

Abstract This study presents 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 of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>α</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>int</mml:mi> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mrow> <mml:mi>LSMO</mml:mi> </mml:mrow> </mml:mrow> </mml:msubsup> <mml:mstyle scriptlevel="0"/> <mml:mo>≈</mml:mo> <mml:mstyle scriptlevel="0"/> <mml:mn>1.4</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> , supporting an extrinsic origin of the high experimental value. Guided by the self-induced inverse spin Hall effect demonstrated in LSMO (Gupta et al 2024 Phys. Rev. B 109 014437), we argue that the large spin Hall angle <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo stretchy="false">|</mml:mo> <mml:msub> <mml:mi>θ</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>SH</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> <mml:mo>≃</mml:mo> <mml:mn>0.093</mml:mn> </mml:mrow> </mml:math> and low longitudinal conductivity of LSMO enable an efficient conversion of spin current to charge current boosting the effective damping. In the LSMO/Pt heterostructures the Pt cap shunts the charge current, raising σ xx and reducing the interfacial <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo stretchy="false">|</mml:mo> <mml:msub> <mml:mi>θ</mml:mi> <mml:mrow> <mml:mrow> <mml:mi>SH</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> </mml:math> to 0.007. A Valet–Fert analysis for layer-resolved ab-initio spin accumulation gives the Pt spin-diffusion length and a non-negligible antidamping SOT coefficient, qualitatively accounting for the observed damping reduction under current bias. The seemingly anomalous damping hierarchy is thus reconciled without invoking additional interfacial mechanisms. The distinct length scales governing spin-pumping normalization, namely, the short absorption depth relevant to self-pumping in a single LSMO film versus the full magnetic thickness applicable to an LSMO/Pt bilayer, are crucial in this context. This observation suggests a practical design strategy: by simultaneously tuning the spin Hall-to-longitudinal conductivity ratio and the spin-diffusion length, one can engineer heterostructures with minimized magnetic losses for spin–orbitronics applications.