  Time-resolved imaging reveals that the helicity dependent all-optical
switching (HD-AOS) of Co/Pt ferromagnetic multilayers proceeds by two stages.
First one involves the helicity independent and stochastic nucleation of
reversed magnetic domains. At the second stage circularly polarized light
breaks the degeneracy between the magnetic domains and promotes the preferred
direction of domain wall (DW) motion. The growth of the reversed domain from
the nucleation cite, for a particular helicity, leads to full magnetic
reversal. This study demonstrates a novel mechanism of HD-AOS mediated by the
deterministic displacement of DWs.
