  We present the results of experimental investigations of magnetic switching
and magnetotransport in a new generation of magnetic devices containing
artificially patterned domains. Our devices are realised by locally reducing
the coercive field of a perpendicularly magnetised Pt (3.5 nm)/Co (0.5 nm)/Pt
(1.6 nm) trilayer structure using a gallium focused ion beam (FIB). Artificial
domain walls are created at the interfaces between dosed and undosed regions
when an external magnetic field switches the former but not the latter. We have
exploited this property to create stripe-like domains with widths down to
sub-micron lengthscales, separated by undosed regions. Using the extraordinary
Hall effect to monitor the local magnetisation we have investigated the
reversal dynamics of these artificial domains by measuring major and minor
hysteresis loops. The coercive field of regions irradiated with identical doses
systematically increases as their size decreases. In the lower branch of minor
loops, reversal is seen to occur via a few large Barkhausen events. Preliminary
measurements of transport across domain walls reveal a positive domain wall
resistance, that does not change sign from 4.2 K to 300 K.
