  It is proposed a novel method of the spectrally selective detection of the
short spin waves (or magnons) by means of the transverse magneto-optical (MO)
intensity effect in transmission in the magnetoplasmonic nanostructure. The
method is based on the analysis of the MO effect spectrum versus the modulation
of the sample magnetization (i.e. spin wave) and related spatial symmetry
breaking in the magnetic layer. The spatial symmetry breaking leads to the
appearance of MO effect modulation at the normal incidence of light in the
spectral range of the optical states (SPP and waveguide modes) and the breaking
of the antisymmetry of the effect with respect to the sign of the incidence
angle of light. Besides it is revealed that the magnitude of the MO effect
varies with respect to the phase shift between the spin wave and the plasmonic
grating as a harmonic function with a period equal to the magnon wavelength.
All these facts allow to detect the spin waves of the certain wavelength
propagating in the nanostructure by measuring of the MO effect in the
nanostructure.
