  Phase diagram and critical properties are studied for three-dimensional
double exchange model with and without quenched disorder. Employing the Monte
Carlo method and the systematic analysis on the finite-size effect, we estimate
the Curie temperature and the critical exponent as functions of the doping
concentration and the strength of the random potential. The Curie temperature
well scales to the kinetic energy of electrons in the ground state as expected
for this kinetics-driven ferromagnetism. The universality class of this
transition is described by the short-range Heisenberg fixed point. The results
are compared with the experimental results in the colossal magnetoresistance
manganites.
