Dynamics of electron-magnon interaction and ultrafast demagnetization in thin iron films

The electronic and spin dynamics in thin iron films have been investigated by means of time-resolved reflectivity and time-resolved magneto-optical Kerr effect. Combining the two techniques, it is possible to clarify the role of electron-phonon and electron-magnon interactions on the ultrafast magnetization dynamics. In particular, we show that the rapid (~100 fs) demagnetization is established at the electronic level through electron-magnon excitation, while the subsequent recovery of the spin order is attributed to the Elliott-Yafet spin-flip scattering process on a time scale slightly shorter than a picosecond. Both processes have characteristic time constants that undoubtedly differ from the measured electron-phonon coupling time of 240 fs.