Phase separation in double-exchange systems

Ferromagnetic systems described by the double-exchange model are investigat ed. At temperatures close to the Curie temperature, and for a wide range of doping levels, the system is unstable toward phase separation. The chemica l potential decreases upon increasing doping, due to the significant depend ence of the bandwidth on the number of carriers. The reduction of the elect ronic bandwidth by spin disorder leads to an enormously enhanced thermopowe r which peaks near T-C, with a sign opposite to that predicted by a rigid-b and model.