Time-resolved magneto-optical imaging reveals that the dynamics of the helicity-dependent all-optical switching (HD-AOS) of Co/Pt ferromagnetic multilayers occurs on the time scales from nanoseconds to seconds. We find HD-AOS proceeds by two stages. First, for an optimized laser fluence, the ultrashort laser pulse demagnetizes the film to 25% of the initial magnetization. Subsequent laser pulses aids nucleation of small reversed domains. The observed nucleation is stochastic and independent of the helicity of laser light. At the second stage circularly polarized light breaks the degeneracy between the magnetic domains promoting a preferred direction of domain wall motion. One circular polarization results in a collapse of the reversed magnetic domains. The other polarization causes the growth of reversed magnetic domain from the nucleation sites, via deterministic displacement of the domain wall resulting in magnetization reversal. This mechanism is supported by further imaging studies of deterministic laser-induced displacement of the domain walls when excited by circularly polarized optical pulses.

Excitation of antiferromagnetic HoFeO₃ with a single 80 fs laser pulse triggers a first-order spin-reorientation phase transition. In the ultrafast kinetics of the transition one can distinguish the processes of impulsive excitation of spin precession, nucleation of the new domain and growth of the nuclei. The orientation of the spins in the nuclei is defined by the phase of the laser-induced coherent spin precession. The growth of the nuclei is further promoted by heating induced by the laser excitation. Hereby we demonstrate that in HoFeO₃ coherent control of the spin precession allows an effective control of the route of the heat-induced first-order magnetic phase transition. The theoretical description of the excitation of the spin precession by linearly-polarized ultrashort laser pulses is developed with the sigma model. The analysis showed high sensitivity of the excited dynamics to the initial spin orientations with respect to the crystallographic axes of the material.