  In this manuscript time-resolved magneto-optical Kerr effect experiments on
structured CoFeB films are presented. The geometries considered are two
dimensional square lattices of micrometer-sized antidots, fabricated by a
focused ion beam. The spin-wave spectra of these magnonic crystals show a novel
precessional mode, which can be related to a Bloch state at the zone boundary.
Additionally, another magnetic mode of different nature appears, whose
frequency displays no dependence on the externally applied magnetic field.
These findings are interpreted as delocalized and localized modes,
respectively.
