  The spin torque exerted on a magnetic moment is a reaction to spin filtering
when spin-polarized electrons interact with a thin ferromagnetic film. We show
that, for certain conditions, a spin transmission resonance (STR) gives rise to
a failure of spin filtering. As a consequence, no spin is transfered to the
ferromagnet. The condition for STR depends on the incoming energy of electrons
and the thickness of the film. For a simple model we find that when the STR
condition is satisfied, the ferromagnetic film is transparent to the incoming
electrons.
