Magnetic phase diagram of the Kondo lattice model with quantum localized spins

The magnetic phase diagram of the ferromagnetic Kondo lattice model is determined at $T=0$ in one-dimension (1D), 2D, and 3D for various magnitudes of the quantum mechanical localized spins ranging from $S=\frac{1}{2}$ to classical spins $(S\ensuremath{\rightarrow}\ensuremath{\infty})$. 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 $S=\frac{1}{2}$, 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.