  Neutron scattering has been used to investigate the evolution of the long-
and short-range charge-ordered (CO), ferromagnetic (FM), and antiferromagnetic
(AF) correlations in single crystals of Pr1-xCaxMnO3. The existence and
population of spin clusters as refected by short-range correlations are found
to drastically depend on the doping (x) and temperature (T). Concentrated spin
clusters coexist with long-range canted AF order in a wide temperature range in
x = 0.3 while clusters do not appear in x = 0.4 crystal. In contrast, both CO
and AF order parameters in the x = 0.35 crystal show a precipitous decrease
below ~ 35 K where spin clusters form. These results provide direct evidence of
magnetic phase separation and indicate that there is a critical doping x_c
(close to x = 0.35) that divides the phase-separated site-centered from the
homogeneous bond-centered or charge-disproportionated CO ground state.
