  The influence of surface plasmons on the magneto-optic activity in a
two-dimensional hexagonal array is addressed. The experiments were performed
using hexagonal array of circular holes in a ferromagnetic Ni film. Well
pronounced troughs are observed in the optical reflectivity, resulting from the
presence of surface plasmons. The surface plasmons are found to strongly
enhance the magneto-optic response (Kerr rotation), as compared to a continuous
film of the same composition. The influence of the hexagonal symmetry of the
pattern on the coupling between the plasmonic excitations is demonstrated,
using optical diffraction measurements and theoretical calculations of the
magneto-optic and of the angular dependence of the optical activity.
