  Magnetization reversal in GdFeCo by circularly polarized light is shown to
occur at the femtosecond time scale. In contrast to the well known
laser-assisted magnetization reversal based on the laser heating, we here
demonstrate that this femtosecond all-optical magnetization reversal is more
efficient at lower temperatures. The lower the temperatures, the smaller the
laser fluence required for the switching. This switching is in agreement with a
more recent theoretical prediction $[ \text{Phys. Lett. A \textbf{372}, 1915
(2008)} ] $ and demonstrates the feasibility of the femtosecond athermal
magnetization reversal.
