Ferrimagnetic alloys are model systems for understanding the ultrafast magnetization switching in materials with antiferromagnetically-coupled sublattices. Here we investigate the dynamics of the rare-earth and transition-metal sublattices in ferrimagnetic GdFeCo and TbCo dots excited by spin-orbit torques with combined temporal, spatial, and elemental resolution. We observe distinct switching regimes in which the magnetizations of the two sublattices either remain syn-6
chronized throughout the reversal process or switch following different trajectories in time and space. In the latter case, we observe a transient ferromagnetic state that lasts up to 2 ns. The asynchronous switching of the two magnetizations is ascribed to the master-agent dynamics induced by the spin-orbit torques in combination with the weak antiferromagnetic coupling, which depends sensitively on the microstructure of ferrimagnets. A larger antiferromagnetic exchange between the two sublattices leads to faster switching and shorter recovery of the magnetization after a current pulse.
