Conduction band filling effects in the Kondo lattice model

The Kondo effect is usually described as the screening of the localized spins by the conduction electrons via an anti ferromagnetic coupling between them. In the case of the Kondo lattice, an "exhaustion" problem arises if the number of conduction electrons is not sufficient to screen all the lattice spins. Here, we discuss a Kondo lattice model with local spins (1)/(2) and a fractional conduction band filling and we take into account both the intrasite Kondo exchange and an intersite antiferromagnetic exchange interaction. This model is treated within an extended mean field method and analytical expressions of the mean field parameters are found for T = 0. We show that the Kondo effect disappears for low band filling and/or strong intersite coupling and a phase diagram is presented as a function of both parameters. (C) 2002 Published by Elsevier Science B.V.