Femtosecond spin dynamics of ferromagnetic thin films and nanodots probed by spin polarized photoemission electron microscopy

We use photoemission electron microscopy to measure the dielectric response of nanostructured CoPt multilayers. The polarization dependence of the spatially resolved two-photon photoemission yield can be directly related to optical laser fields near the edges of the nanodots. Photoelectron spin analysis reveals that enhanced optical near fields can be used to induce a local demagnetization of the sample within 400 fs following fs laser excitation. Experiments on ultrathin Co films demonstrate that for high fluences the observed demagnetization timescale of 130 fs is masked by a novel spin dependent bleaching effect in two-photon photoemission.