  Spectroscopy of magnetization-induced second-harmonic generation (MSHG) is
studied in magnetic Co$_{x}$Ag$_{1-x}$ granular films containing Co
nanoparticles. A strong resonance of the magnetic contrast of the
second-harmonic generation (SHG) intensity is observed in the two-photon energy
range from 3,8 eV to 4,5 eV. The local surface plasmons exited in magnetic Co
nanogranules in this spectral range assist MSHG and are responsible for a
significant enhancement of the SHG magnetic contrast due to the resonances of
local optical fields.
