  We investigate the effect of hole and electron doping to half-filling in the
periodic Anderson model on a triangular lattice by the Hartree-Fock
approximation at zero temperature. At half-filling, the system exhibits a
partially disordered insulating state, in which a collinear antiferromagnetic
order on an unfrustrated honeycomb subnetwork coexists with nonmagnetic state
at the remaining sites. We find that the carrier doping destabilizes the
partially disordered state, resulting in a phase separation to a doped metallic
state with different magnetic order. The partially disordered state is
restricted to the half-filled insulating case, while its metallic counterpart
is obtained as a metastable state in a narrow electron doped region.
