  Ground state magnetic phase diagrams of the square and simple cubic lattices
are investigated for the narrow band Hubbard model within the slave-boson
approach by Kotliar and Ruckenstein. The transitions between saturated
(half-metallic) and non-saturated ferromagnetic phases as well as similar
transition in antiferromagnetic (AFM) state are considered in the
three-dimensional case. Two types of saturated antiferromagnetic state with
different concentration dependences of sublattice magnetization are found in
the two-dimensional case in the vicinity of half-filling: the state with a gap
between AFM subbands and AFM state with large electron mass. The latter state
is hidden by the phase separation in the finite-U case.
