Ultrafast three-dimensional magnetization precession and magnetic anisotropy of a photoexcited thin film of iron

We investigated the three-dimensional dynamics of the magnetization vector launched by an intense infrared pulse of femtosecond duration in a thin Fe film. We demonstrate how a single experiment of time-resolved magneto-optical Kerr effect can provide quantitative information on the temporal evolution of the magnetization trajectory. Our approach allows us to follow the precessional motion of the magnetization and to retrieve the modulus and orientation of the magnetocrystalline anisotropy field as a function of time-and therefore of the local temperature-providing a direct experimental evidence of the phenomenological mechanism triggering the magnetization precession.