  We have investigated the magnetic and magnetotransport properties of
Ba$_2$FeMoO$_6$ thin films produced by pulsed laser deposition from optimized
bulk material. The films are comprised of grains of crystalline Ba$_2$FeMoO$_6$
with a disordered grain boundary region that lowers the net saturation
magnetization of the film and prevents full magnetic alignment below a Curie
temperature $T_C$$\sim$305 K. Magnetotransport measurements point to the
Ba$_2$FeMoO$_6$ grains retaining the high spin polarization of a half-metal up
to $T_C$, while the grain boundaries greatly reduce the spin polarization of
the intergrain electrical current due to spin-flip scattering. Our results show
that a strong spin polarization of the electronic charge carriers is present
even in Ba$_2$FeMoO$_6$ films that do not show the ideal bulk magnetic
character.
