  The nonlinear magneto-plasmonics aims to utilize plasmonic excitations to
control the mechanisms and taylor the efficiencies of the non-linear light
frequency conversion at the nanoscale. We investigate the mechanisms of
magnetic second harmonic generation in hybrid gold-cobalt-silver multilayer
structures, which support propagating surface plasmon polaritons at both
fundamental and second harmonic frequencies. Using magneto-optical spectroscopy
in Kretschmann geometry, we show that the huge magneto-optical modulation of
the second harmonic intensity is dominated by the excitation of surface plasmon
polaritons at the second harmonic frequency, as shown by tuning the optical
wavelength over the spectral region of strong plasmonic dispersion. Our
proof-of-principle experiment highlights bright prospects of nonlinear
magneto-plasmonics and contributes to the general understanding of the
nonlinear optics of magnetic surfaces and interfaces.
