Not yet reviewed by Pith; the record is open.

While nearly single cycle THz pulse is conventionally accepted as the stimulus for the fastest and the most energy efficient control of spins in magnets, all-dielectric metasurfaces have been recently demonstrated to be the least dissipative mean to enhance and control the coupling of light to spins. All-dielectric metasurfaces for the THz control of spins hold great potential in the field of spintronics and related technologies, pushing the boundaries of speed and energy efficiency in spin-based information processing. Here we demonstrate such a metasurface for an advanced THz control of spins in a ferrimagnetic film of iron garnet. Structuring a nonmagnetic substrate one can force a THz electromagnetic field, otherwise described by plane waves, to acquire an out-of-plane magnetic field and thus enable arbitrary direction of the torque acting on spins in all three dimensions. Hence, metaphotonics opens up a plethora of opportunities for advanced control of spins at THz rates in many hot fields of contemporary science, including spintronics, magnonics and quantum computing.