  We investigate the Kondo Lattice Model on 2D clusters using the Finite
Temperature Lanczos Method. The temperature dependence of thermodynamic and
correlations functions are systematically studied for various Kondo couplings
JK. The ground state value of the total local moment is presented as well.
Finally, the phase diagrams of the finite clusters are constructed for periodic
and open boundary conditions. For the two boundary conditions, two different
regimes are found for small JK/t, depending on the distribution of
non-interacting conduction electron states. If there are states within JK
around the Fermi level, two energy scales, linear and quadratic in JK, exist.
The former is associated with the onsite screening and the latter with the RKKY
interaction. If there are no states within JK around the Fermi level, the only
energy scale is that of the RKKY interaction. Our results imply that the form
of the electron density of states (DOS) plays an important role in the
competition between the Kondo screening and the RKKY interaction. The former is
stronger if the DOS is larger around the Fermi level, while the latter is less
sensitive to the form of the DOS.

Strongly Correlated Electrons;Mesoscale and Nanoscale Physics