Development of L10-ordered FePt with low damping and large perpendicular magnetic anisotropy by engineering the nanostructure

THz spintronics is an emergent area of research aimed at bridging the gap between fifth- and sixth-generation wireless telecommunications by utilizing spintronic devices such as magnetic spin torque oscillators as a source of low powered THz emission. The realization of such devices using ferromagnetic metal thin films however requires magnetic materials with both large perpendicular magnetic anisotropy (PMA) and low Gilbert damping constants. In this Letter, we report on the development of L10-ordered FePt with an effective Gilbert damping constant as low as 0.033. Using time-resolved magneto-optical Kerr effect, we characterized the magnetization dynamics of continuous L10-ordered FePt grown on MgO and SrTiO3 substrates. By changing the substrate on which FePt is grown, the lattice mismatch and subsequent number of misfit dislocations at the interface and L10-ordering can be controlled. We found that fewer misfits and improved ordering in FePt lead to a reduced Gilbert damping constant due to reduced electron scattering but that FePt grown on SrTiO3 also shows robust perpendicular magnetic anisotropy. Importantly, these results demonstrate the ability to control the damping in FePt and similar materials by changing the number of misfit dislocations at the interface and the smaller damping in FePt opens up the possibility of using this material in spintronic materials in the THz wave range.