  The double-exchange model, which has been extensively studied in the context
of colossal magneto-resistance in perovskite manganese oxides, is known to
exhibit a ferromagnetic metallic state at low temperatures because of the
interplay between localized moments and itinerant electrons through the
Hund's-rule coupling. Here we investigate numerically the ferromagnetic
transition in the double-exchange model defined on the frustrated pyrochlore
lattice as a simple model for ferromagnetic pyrochlore oxides. We demonstrate
that the finite-size corrections are largely reduced by implementing averages
over the twisted boundary conditions in the Monte Carlo simulation, which
enables to estimate the ferromagnetic transition temperature in relatively
small size clusters. The estimate is compared with that for the non-frustrated
cubic lattice system.
