  Magnetoplasmonics exploits interactions between light and magnetic matter at
the nanoscale for light manipulation and resonant magneto-optics. One of the
great challenges of this field is overcoming optical losses in magnetic metals.
Here we exploit surface plasmon polaritons (SPPs) excited at the interface of a
SiO2/Au bilayer to induce strong magneto-optical responses on the Ni nanodisks
of a periodic array. Using a reference system made of Au nanodisks, we show
that optical losses in Ni do hardly broaden the linewidth of SPP-driven
magneto-optical signals. Loss mitigation is attained because the free electrons
in the Ni nanodisks are driven into forced oscillations away from their plasmon
resonance. By varying the SiO2 layer thickness and lattice constant of the Ni
nanodisk array, we demonstrate tailoring of intense magneto-optical Kerr
effects with a spectral linewidth down to ~25 nm. Our results provide important
hints on how to circumvent losses and enhance magneto-optical signals via the
design of off-resonance magnetoplasmonic driving mechanisms.
