Influence of the Kondo effect on spin density waves in the Kondo lattice model

•We compare the isotropic and Ising spin Kondo lattice model.•We show the importance of the Kondo effect in the isotropic model for the large Fermi surface SDW, paramagnetic phase, and the quantum phase transition.•In the Ising spin Kondo lattice model the small Fermi surface SDW phase exists for any interaction strength.

We analyze the influence of the Kondo effect on the spin density wave (SDW) phase in the Kondo lattice model (KLM) for a two-dimensional square lattice. We demonstrate that in the isotropic KLM the SDW phase is divided into a small Fermi-surface region and a large Fermi-surface region and vanishes for strong interaction. On the other hand, in the Ising-spin KLM, where the Kondo effect is absent, we only find a small Fermi-surface SDW phase, which does not vanish at strong coupling. This demonstrates the importance of the Kondo effect for the large Fermi surface SDW phase as well as for the existence of the quantum critical transition between the SDW phase and the paramagnetic phase.