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Using the dynamical mean-field theory, we have evaluated the magnetic instabilities and T=0 phase diagram of the double-exchange model on a Bethe lattice in infinite dimensions. In addition to ferromagnetic (FM) and antiferromagnetic (AF) phases, we also study a class of disordered phases with magnetic short-range order (SRO). In the weak-coupling limit, a SRO phase has a higher transition temperature than the AF phase for all fillings p below 1 and can even have a higher transition temperature than the FM phase. At T=0 and for small Hund's coupling JH, a SRO state has lower energy than either the FM or AF phases for 0.26≤p<1. Phase separation is absent in the JH →0 limit but appears for any nonzero value of JH. © 2006 The American Physical Society.

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Physical Review B - Condensed Matter and Materials Physics