Ferromagnetism of the Kondo Lattice Model in the Classical Spin Limit

Ferromagnetism of the Kondo lattice model (KLM) in the classical spin limit has been studied by using the single site approximation in the functional integral method. The magnetic phase diagram of the ground state is qualitatively consistent with one predicted by Ueda et al., except for a small Hund coupling limit where we have found the ferromagnetic phase for a finite electron concentration range of 0<n<0.4. The Curie temperature for the small n region is found to behave proportionally to n^1/3 J² Further for small n the localized spin system exhibits snake-type M-Tcurve which is often the case with one with the mean field approximation for the Heisenberg model under the external magnetic field. This reflects that the KLM is composed of two systems, localized spin and conduction electron systems, coupled each other.