  Plasmonics has been attracting considerable interest as it allows
localization of light at nanoscale dimensions. A breakthrough in integrated
nanophotonics can be obtained by fabricating plasmonic functional materials.
Such systems may show a rich variety of novel phenomena and also have huge
application potential. In particular magnetooptical materials are appealing as
they may provide ultrafast control of laser light and surface plasmons via an
external magnetic field. Here we demonstrate a new magnetooptical material: a
one-dimensional plasmonic crystal formed by a periodically perforated noble
metal film on top of a ferromagnetic dielectric film. It provides giant Faraday
and Kerr effects as proved by the observation of enhancement of the transverse
Kerr effect near Ebbesen's extraordinary transmission peaks by three orders of
magnitude. Surface plasmon polaritons play a decisive role in this enhancement,
as the Kerr effect depends sensitively on their properties. The plasmonic
crystal can be operated in transmission, so that it may be implemented in
devices for telecommunication, plasmonic circuitry, magnetic field sensing and
all-optical magnetic data storage.
