  We report on the manipulation of magnetization by femtosecond laser pulses in
a periodic array of cylindrical nickel nanoparticles. By performing experiments
at different wavelength, we show that the excitation of collective surface
plasmon resonances triggers demagnetization in zero field or magnetic switching
in a small perpendicular field. Both magnetic effects are explained by
plasmon-induced heating of the nickel nanoparticles to their Curie temperature.
Model calculations confirm the strong correlation between the excitation of
surface plasmon modes and laser-induced changes in magnetization.
