Electron-Phonon Coupling Parameter of Ferromagnetic Metal Fe and Co

The electron-phonon coupling (g) parameter plays a critical role in the ultrafast transport of heat, charge, and spin in metallic materials. However, the exact determination of the g parameter is challenging because of the complicated process during the non-equilibrium state. In this study, we investigate the g parameters of ferromagnetic 3d transition metal (FM) layers, Fe and Co, using time-domain thermoreflectance. We measure a transient increase in temperature of Au in an FM/Au bilayer; the Au layer efficiently detects the strong heat flow during the non-equilibrium between electrons and phonons in FM. The g parameter of the FM is determined by analyzing the temperature dynamics using thermal circuit modeling. The determined g values are 8.8-9.4 × 10¹⁷ W m^-3 K^-1 for Fe and 9.6-12.2 × 10¹⁷ W m^-3 K^-1 for Co. Our results demonstrate that all 3d transition FMs have a similar g value, in the order of 10¹⁸ W m^-3 K^-1.