PHASE-DIAGRAM OF THE DOUBLE EXCHANGE MODEL

We develop a functional integral formulation for the double exchange m odel with an infinitely large Hund's coupling, in which the local quan tum spins are described by the CP1 spinor field. This formulation dire ctly connects the quantum approach with classical approximation. The s pin wave dynamics and the magnetic phase transition are studied by usi ng a mean field approximation. The Curie temperature T-c obtained is c omparable to the experimental values in the manganese oxides. An insta bility of the uniform electron states against charge fluctuations caus ed by many-body correlation effect is also reported.