Keywords:Ultrafast spin dynamics, spin plasmonics, inverse Faraday effect
Ultrafast all-optical control of spins with femtosecond laser pulses is a trending topic at the crossroads of photonics and magnetism with a direct impact on future magnetic recording. It is now widely accepted that the future of high-density all-optical magnetic recording depends on the achievements of sub-diffractional nanophotonics featuring light localization on the nanoscale by surface plasmon resonances. As such, the fundamental understanding of the interactions of high-frequency coherent spin dynamics with plasmonic excitations on both nanometer and subpicosecond scales in opto-magnonic media is highly desirable. Here, we show that surface plasmon-polaritons in hybrid metal-dielectric structures can provide spatial confinement of the inverse Faraday effect, mediating the excitation of localized coherent spin precession with 0.41-THz frequency. We demonstrate two orders of magnitude enhancement of the excitation efficiency at the surface plasmon resonance within a 100-nm layer of a dielectric garnet.