Thermal coupling parameters between electron, phonon, and magnon of Nickel

Thermal interaction in an electron-phonon-magnon system in a ferromagnetic Ni film is investigated using a time-resolved pump-probe technique with thermoreflectance and magneto-optical Kerr effect. A nanoscale Au/Ni bilayer is used to induce thermal excitation of Ni in two ways: direct heating of Ni and indirect heating of Ni via Au. By comparing experiments and thermal modeling, we obtain the coupling parameters for electron-phonon, electron-magnon, and phonon-magnon pairs: 8.55 × 10¹⁷, 1.0–1.3 × 10¹⁷, and 0.8–1.1 × 10¹⁷ W m⁻³ K⁻¹, respectively. In particular, we find that the phonon-magnon coupling parameter plays a significant role as a fast heat dissipation channel from magnon to phonon during the initial few picoseconds. In addition, both direct and indirect heating can be explained by similar coupling parameters with a variation less then 30%. Consequently, we conclude that the heat exchange between electron, phonon, and magnon is the dominant mechanism for the ultrafast demagnetization.