We present the study of magnetization, thermal expansion, specific heat,
resistivity, and a.c. susceptibility of
(Pr1βyβEuyβ)0.7βCa0.3βCoO3β cobaltites. The measurements were
performed on ceramic samples with y=0.12β0.26 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 (16O by 18O) 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 Co4+ ions, which favor the formation of the intermediate-spin state of
neighboring Co3+ ions.Comment: 13 pages, including 11 figures, to be published in Phys. Rev.