  The ground-state magnetic phase diagram is calculated within the Hubbard and
$s$-$d$ exchange (Kondo) models for square and simple cubic lattices vs. band
filling and interaction parameter. The difference of the results owing to the
presence of localized moments in the latter model is discussed. We employ a
generalized Hartree-Fock approximation (HFA) to treat commensurate
ferromagnetic (FM), antiferromagnetic (AFM), and incommensurate (spiral)
magnetic phases. The electron correlations are taken into account within the
Hubbard model by using the Kotliar-Ruckenstein slave boson approximation (SBA).
The main advantage of this approach is a correct qualitative description of the
paramagnetic phase: its energy becomes considerably lower as compared with HFA,
and the gain in the energy of magnetic phases is substantially reduced.
