Ultrafast magnetization dynamics investigated in real space (invited)

The ultrafast magnetization dynamics induced in ferromagnetic thin films by femtosecond optical pulses is investigated in real space. Our experimental method allows us to retrieve the three-dimensional trajectory of the magnetization vector over a large temporal range, from ∼100fsto∼1ns. This approach carries important information both on the initial spin dynamics and the magnetization precession. An ultrafast decrease of the magnetization modulus, occurring within ∼100fs, reveals the initial laser induced demagnetization. It is accompanied by a reorientation of the magnetization vector, taking place during the first picosecond, a process which strongly depends on the material anisotropy. Finally, the three-dimensional trajectory of the magnetization during its precession and damping undertakes a complex pathway as the magnetization modulus varies until the energy is dissipated to the environment in the nanosecond time scale.