  The recently discovered magnetization reversal driven solely by a femtosecond
laser pulse has been shown to be a promising way to record information at
record breaking speeds. Seeking to improve the recording density has raised
intriguing fundamental question about the feasibility to combine the ultrafast
temporal with sub-wavelength spatial resolution of magnetic recording. Here we
report about the first experimental demonstration of sub-diffraction and
sub-100 ps all-optical magnetic switching. Using computational methods we
reveal the feasibility of sub-diffraction magnetic switching even for an
unfocused incoming laser pulse. This effect is achieved via structuring the
sample such that the laser pulse experiences a passive wavefront shaping as it
couples and propagates inside the magnetic structure. Time-resolved studies
with the help of photo-emission electron microscopy clearly reveal that the
sub-wavelength switching with the help of the passive wave-front shaping can be
pushed into sub-100 ps regime.
