Temperature-dependent perpendicular anisotropy and Gilbert damping of L10−FePd films: Role of noble-metal buffer layers

Abstract

The moderate bulk perpendicular magnetic anisotropy (PMA, ${K}_{\mathrm{u}}\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}1\phantom{\rule{0.16em}{0ex}}\mathrm{MJ}/{\mathrm{m}}^{3}$) and low Gilbert damping (\ensuremath{\alpha} 0.01) make $L{1}_{0}$-FePd a promising candidate for energy-efficient and nonvolatile spintronic devices with large areal densities (down to 5-nm pitch sizes or even lower). Existing applications subject spintronic devices to a wide range of operating temperatures (e.g., \ensuremath{-}55 to 150 \ifmmode^\circ\else\textdegree\fi{}C). To better address the technological viability of FePd for spintronic applications, it is of utmost importance to evaluate the material performance of $L{1}_{0}$-FePd (e.g., anisotropy strength and Gilbert damping) at elevated temperatures. In this work, we systematically investigate the effect of buffer layers (Cr/Pt, Cr/Ru, Cr/Rh, Cr/Ir, and Ir) on the PMA and Gilbert damping of $L{1}_{0}$-FePd from room temperature (RT, 25 \ifmmode^\circ\else\textdegree\fi{}C) to 150 \ifmmode^\circ\else\textdegree\fi{}C using the time-resolved magneto-optical Kerr effect metrology. It is found that the effective anisotropy field (${H}_{\mathrm{k},\mathrm{eff}}$) of FePd decreases with the testing temperature (${T}_{\mathrm{test}}$) and the ratio of ${H}_{\mathrm{k},\mathrm{eff}}$(150 \ifmmode^\circ\else\textdegree\fi{}C)/${H}_{\mathrm{k},\mathrm{eff}}$(25 \ifmmode^\circ\else\textdegree\fi{}C) is positively correlated to the degree of $L{1}_{0}$ phase ordering. The Gilbert damping of $L{1}_{0}$-FePd either increases with ${T}_{\mathrm{test}}$ or stays nearly constant over the ${T}_{\mathrm{test}}$ range. We attribute the temperature dependence of Gilbert damping to the spin diffusion length of the metallic buffer layer (\ensuremath{\lambda}), presumably through the spin pumping effect. Results of this work provide guidance to tailor $L{1}_{0}$-FePd properties through buffer layer engineering for applications in spintronic devices over wide operating temperature ranges.