Abstract

A few years ago, it has been demonstrated that it is possible to demagnetize ferromagnetic metallic thin films using femtosecond optical pulses [1]. The magnetization dynamics of Ni and CoPt metallic films was then investigated with time resolved Kenmeasurements as a function of applied magnetic field and laser intensity when the materials undergoes its feno-paramagnetic phase transition. These observations have been confirmed with a variety of femtosecond techniques like for example the second order nonlinear Ken effect [2] or spin resolved two photon photoemission [3]. More recently, we have shown that, under a weak perturbation of the magnetization with pulses of 20 fs duration, the initial ultrafast spin dynamics follows the thermalization of the electronic populations to a Fermi-Dirac distribution [4], In this paper, we report the first observation of a coherent exchange of energy between the spins and the lattice while both populations are cooling down.

© 2002 Optical Society of America