  Phase diagram of an Ising-spin Kondo lattice model on a triangular lattice
near 1/3-filling is investigated by Monte Carlo simulation. We identify a
partially disordered phase with coexistence of magnetic order and paramagnetic
moments, which was unstable in two-dimensional Ising models with localized
spins only. The partial disorder emerges in the competing regime between a
twosublattice stripe phase and three-sublattice ferrimagnetic phase, at finite
temperatures above an electronic phase separation. The peculiar magnetic
structure accompanies a charge order and develops a gap in the electronic
structure. The results manifest a crucial role of the nonperturbative interplay
between spin and charge degrees of freedom in stabilizing the partial disorder.
