  Magnetic and electronic properties of a Kondo lattice model with Ising
localized spins are studied on an isotropic triangular lattice. By using Monte
Carlo simulation, we present that the model shows a rich phase diagram with
four dominant states: two-sublattice stripe, three-sublattice ferrimganetic,
partially disordered, and Kosterlitz-Thouless like quasi-long-range ordered
states. Among them, the partially disordered state and Kosterlitz-Thouless like
state are intermediate phases induced by thermal fluctuations in the phase
competing regime; they are present only at finite temperatures and eventually
taken over by another phases as the temperature is further lowered. Although
the Kosterlitz-Thouless like state was found also in triangular Ising
antiferromagnets with further-neighbor interactions, the partially disordered
state has not been reported in the localized spin only models in two
dimensions. Interestingly, the partially disordered phase is also peculiar in
the charge degree of freedom of itinerant electrons; it is insulating and
accompanied by charge disproportionation. From a combined analysis of a
mean-field calculation of the band structure and Monte Carlo simulation, we
conclude that the partial disorder in the present model is stabilized by the
Slater mechanism.
