Coexistence of magnetic order and Kondo effect in the Kondo-Heisenberg model

The Kondo lattice model is investigated through a fermionic mean-field approximation. The obtained phase diagram, including the pure ferromagnetic (FM), antiferromagnetic (AF), Kondo (K), and mixed phases, is in good agreement with previous studies. Calculations on the simple cubic and square lattices confirm a robust coexistence of ferromagnetism and Kondo effect (FM + K), sustained by a partial Kondo screening, which leads to the concept of a spin selective Kondo insulator. We have also obtained a coexistence of antiferromagnetism and Kondo effect (AF+K), which requires the intervenience of a next-nearest-neighbor hopping t' and a Heisenberg exchange J(ij). The effect of temperature and pressure is described by the behavior of the order parameters. The corresponding Neel temperature T-N and Kondo temperature T-K are plotted in the form of a Doniach diagram. The presence of the intermediate mixed phases is fundamental to determine the order of the magnetic phase transitions as one approaches the quantum critical point.