Terahertz emission from a spintronic stack nanodecorated with plasmonic nanoparticles

Spintronic emitters promise to revolutionise terahertz (THz) sources by converting ultrafast optical pulses into broadband THz radiation without phase-matching constraints. Because the conversion relies on spin-current injection across a nanometre-thin magnetic layer, its efficiency is ordinarily limited by weak optical coupling. Here, we present a demonstration of a drop-casting based approach to introduce ultrafast plasmonic-mediated coupling: a sparse-layer of silica–gold core–shell nanoparticles is deposited directly onto a W/Fe/Pt spintronic trilayer. This sparse (≈ 6%) decoration leads to a measured enhancement of the emitted THz peak field between 1.1x and 1.6x relative to the bare stack as the angle is increased from 0° to 75°, pointing to a very high local conversion enhancement for this low-coverage spintronic emitter compared with the bare stack, with the maximum emission reached at 0°. This demonstration points to a viable pathway toward highly efficient spintronic terahertz emitters with potential applications in spectroscopy, imaging, and ultrafast technologies.