  The magnetic phase diagram of the ferromagnetic Kondo lattice model is
determined at T=0 in 1D, 2D, and 3D for various magnitudes of the quantum
mechanical localized spins ranging from S=1/2 to classical spins. We consider
the ferromagnetic phase, the paramagnetic phase, and the
ferromagnetic/antiferromagnetic phase separated regime. There is no significant
influence of the spin quantum number on the phase boundaries except for the
case S=1/2, where the model exhibits an instability of the ferromagnetic phase
with respect to spin disorder. Our results give support, at least as far as the
low temperature magnetic properties are concerned, to the classical treatment
of the S=3/2-spins in the intensively investigated manganites, for which the
ferromagnetic Kondo-lattice model is generally employed to account for
magnetism.
