  We studied magnetic properties of the double exchange (DE) model with S=1/2
localized spins at T=0, using exact diagonalization in the framework of the
dynamical mean field theory. Obtained phase diagram contains ferromagnetic,
antiferromagnetic and paramagnetic phases. Comparing the phase diagram with
that of the DE model with classical localized spins, we found that the quantum
fluctuations of localized spins partly destabilize the ferromagnetism and
expand the paramagnetic phase region. We found that phase separations occur
between the antiferromagnetic and paramagnetic phases as well as the
paramagnetic and ferromagnetic ones.
