  Magnetic field driven domain wall dynamics in a ferrimagnetic GdFeCo thin
film with perpendicular magnetic anisotropy is studied using low temperature
magneto-optical Kerr microscopy. Measurements performed in a practically
athermal condition allow for the direct experimental determination of the
velocity ($ \beta = 0.30 \pm 0.03 $) and correlation length ($ \nu = 1.3 \pm
0.3 $) exponents of the depinning transition. The whole family of exponents
characterizing the transition is deduced, providing evidence that the depinning
of magnetic domain walls is better described by the quenched Edwards-Wilkinson
universality class.
