  A new mechanism for ferromagnetism in CeRh_3B_2 is proposed on the basis of
variational Monte Carlo results. In a one-dimensional Anderson lattice where
each 4f electron hybridizes with a ligand orbital between neighboring Ce sites,
ferromagnetism is stabilized due to a nearly flat band which is a mixture of
conduction and 4f electron states. Because of the strong spin-orbit interaction
in 4f electron states, and of considerable amount of hybridization in the
nearly flat band, the magnetic moments from 4f and conduction electrons tend to
cancel each other. The resultant ferromagnetic moment becomes smaller as
compared with the local 4f moment, and the Fermi surface in the ferromagnetic
ground state is hardly affected by the presence of 4f electrons. These
theoretical results are consistent with experimental observations in CeRh_3B_2
by neutron scattering and dHvA effects.
