  We propose a novel interaction-based route to half-metal state for
interacting electrons on two-dimensional lattices. Magnetic field applied
parallel to the lattice is used to tune one of the spin densities to a
particular commensurate with the lattice value in which the system
spontaneously `locks in' via van Hove enhanced density wave state. Electrons of
opposite spin polarization retain their metallic character and provide for the
half-metal state which, in addition, supports magnetization plateau in a finite
interval of external magnetic field. Similar half-metal state is realized in
the finite-U Hubbard model on a triangular lattice at 1/3 of the maximum
magnetization.
