We present a microscopic investigation of how the magnetic domain structure in ultrathin films changes after
direct excitation by single ultrashort laser pulses. Using photoelectron emission microscopy in combination with
x-ray magnetic circular dichroism in the resonant absorption of soft x rays, we find that individual laser pulses of
≈60 fs duration and a central wavelength of 800 nm lead to clear changes in the domain structure of a Co layer
of three atomic monolayers thickness in an epitaxial Co/Cu/Ni trilayer on a Cu(001) single-crystal substrate.
A relatively small enhancement of the sample base temperature by 40 K is sufficient to lower the threshold of
laser fluence for domain wall motion by about a factor of two. Pump-probe measurements with a laser fluence
just below this threshold indicate that the laser-induced demagnetization of the sample is far from complete
in these experiments. Although the domain wall motion appears similar to thermal domain wall fluctuations,
quantitatively it cannot be explained by pure thermal activation of domain wall motion by the transient rise of
sample temperature after the laser pulse, but it is likely to be triggered by a laser-induced depinning of domain
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