MONTE-CARLO SIMULATIONS FOR THE MAGNETIC PHASE-DIAGRAM OF THE DOUBLE-EXCHANGE HAMILTONIAN

We have used Monte Carlo simulation techniques to obtain the magnetic phase diagram of the double-exchange Hamiltonian. We have found that t he Berry phase of the hopping amplitude has a negligible effect in the value of the magnetic critical temperature. To avoid finite size prob lems in our simulations we have also developed an approximated express ion for the double-exchange energy. This allows us to obtain the criti cal temperature for the ferromagnetic to paramagnetic transition more accurately. In our calculations we do not observe any strange behavior in the kinetic energy, chemical potential, or electron density of sta tes near the magnetic critical temperature. Therefore. we conclude tha t other effects, not included in the double-exchange Hamiltonian, are needed in order to understand the metal-insulator transition which occ urs in the manganites.