Ferromagnetic transition in three-dimensional double-exchange models is
studied by the Monte Carlo method. Critical temperature Tc is
precisely determined by finite-size scaling analysis. Strong spin fluctuations
in this itinerant system significantly reduce Tc from mean-field
estimates. By choosing appropriate parameters, obtained values of Tc
quantitatively agree with experiments for the ferromagnetic metal regime of
(La,Sr)MnO3, which is a typical perovskite manganite showing colossal
magnetoresistance. This indicates that the double-exchange mechanism alone is
sufficient to explain Tc in this material. Critical exponents are also
discussed.Comment: 4 pages including 1 table and 4 figures, to be published in J. Phys.
Soc. Jp