Abstract
The low-energy spectrum of the ferromagnetic Kondo lattice model on an N-site complete graph extended with on-site repulsion is obtained from the underlying spl(2,1) algebra properties in the strong coupling limit. The ferromagnetic ground state is realized for 1 and N+1 electrons only. We identify the large density of states to be responsible for the suppression of the ferromagnetic state and argue that a similar situation is encountered in the Kagomé, pyrochlore, and other lattices with flat bands in their one-particle density of states.