  The magnetic phase transition is experimentally known to give rise to an
anomalous temperature-dependence of the electron resistivity in ferromagnetic
crystals. Phenomenological theories based on the interaction between itinerant
electron spins and lattice spins have been suggested to explain these
observations. In this paper, we show by extensive Monte Carlo (MC) simulation
the behavior of the resistivity of the spin current calculated as a function of
temperature ($T$) from low-$T$ ordered phase to high-$T$ paramagnetic phase in
a ferromagnetic film. We analyze in particular effects of film thickness,
surface interactions and different kinds of impurities on the spin resistivity
across the critical region. The origin of the resistivity peak near the phase
transition is shown to stem from the existence of magnetic domains in the
critical region. We also formulate in this paper a theory based on the
Boltzmann's equation in the relaxation-time approximation. This equation can be
solved using numerical data obtained by our simulations. We show that our
theory is in a good agreement with our MC results. Comparison with experiments
is discussed.
