  We report a study in which Andreev reflection using a Nb point contact is
used to measure the transport spin polarisation of the 4d itinerant ferromagnet
SrRuO3. By performing the study in high quality thin films with residual
resistivities less than 7micro-ohm-cm, we ensure that the study is done in the
ballistic limit, a regime which is difficult to reach in oxide ferromagnets.
The degree of transport spin polarisation that we find is comparable to that of
the hole doped rare-earth manganites. We conclude that the large transport spin
polarisation results mainly from a difference in the Fermi velocities between
the majority and minority spin channels in this material.
