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Starting from the two-orbital Kondo-lattice model with classical t2g spins, an effective spinless fermion model is derived for strong Hund coupling JH with a projection technique. The model is studied by Monte Carlo simulations and analytically using a uniform hopping approximation. The results for the spinless fermion model are in remarkable agreement with those of the original Kondo-lattice model, independent of the carrier concentration, and even for moderate Hund coupling JH . Phase separation, the phase diagram in uniform hopping approximation, as well as spectral properties including the formation of a pseudo-gap are discussed for both the Kondo-lattice and the effective spinless fermion model in one and three dimensions.

We study the ferromagnetic Kondo model with classical corespins via unbiased Monte-Carlo simulations and derive a simplified model for the treatment of the corespins at any temperature. Our simplified model captures the main aspects of the Kondo model and can easily be evaluated both numerically and analytically. It provides a better qualitative understanding of the physical features of the Kondo model and rationalizes the Monte-Carlo results including the spectral density A k (ω) of a 1D chain with nearest neighbor Coulomb repulsion. By calculating the specific heat and the susceptibility of systems up to size 16 3 , we determine the Curie temperature of the 3D one-orbital double-exchange model, which agrees with experimental values.

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