  We present the study of magnetization, thermal expansion, specific heat,
resistivity, and a.c. susceptibility of
(Pr$_{1-y}$Eu$_y$)$_{0.7}$Ca$_{0.3}$CoO$_3$ cobaltites. The measurements were
performed on ceramic samples with $y = 0.12 - 0.26$ and $y = 1$. Based on these
results, we construct the phase diagram, including magnetic and spin-state
transitions. The transition from the low- to intermediate-spin state is
observed for the samples with $y > 0.18$, whereas for a lower Eu-doping level,
there are no spin-state transitions, but a crossover between the ferromagnetic
and paramagnetic states occurs. The effect of oxygen isotope substitution along
with Eu doping on the magnetic/spin state is discussed. The oxygen-isotope
substitution ($^{16}$O by $^{18}$O) is found to shift both the magnetic and
spin-state phase boundaries to lower Eu concentrations. The isotope effect on
the spin-state transition temperature ($y > 0.18$) is rather strong, but it is
much weaker for the transition to a ferromagnetic state ($y < 0.18$). The
ferromagnetic ordering in the low-Eu doped samples is shown to be promoted by
the Co$^{4+}$ ions, which favor the formation of the intermediate-spin state of
neighboring Co$^{3+}$ ions.
