Critical temperature of ferromagnetic transition in three-dimensional double-exchange models

Ferromagnetic transition in three-dimensional double-exchange models is studied by the Monte Carlo method. Critical temperature T-c is precisely determined by finite-size scaling analysis. Strong spin fluctuations in this itinerant system significantly reduce T-c from mean-field estimates. By choosing appropriate parameters, obtained values of T-c 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 T-c in this material. Critical exponents are also discussed.