  The electric, magnetic, and thermal properties of three perovskite cobaltites
with the same 30% hole doping and ferromagnetic ground state were investigated
down to very low temperatures. With decreasing size of large cations, the
ferromagnetic Curie temperature and spontaneous moments of cobalt are gradually
suppressed - $T_C=130$ K, 55 K and 25 K and $m = 0.68 \mu_B$, 0.34 $\mu_B$ and
0.23 $\mu_B$ for Nd$_{0.7}$Sr$_{0.3}$CoO$_3$, Pr$_{0.7}$Ca$_{0.3}$CoO$_3$ and
Nd$_{0.7}$Ca$_{0.3}$CoO$_3$, respectively. The moment reduction with respect to
moment of the conventional ferromagnet La$_{0.7}$Sr$_{0.3}$CoO$_3$ ($T_C=230$
K, $m = 1.71 \mu_B$) in so-called IS/LS state for Co$^{3+}$/Co$^{4+}$, was
originally interpreted using phase-separation scenario. Based on the present
results, mainly the analysis of Schottky peak originating in Zeeman splitting
of the ground state Kramers doublet of Nd$^{3+}$, we find, however, that
ferromagnetic phase in Nd$_{0.7}$Ca$_{0.3}$CoO$_3$ and likely also
Pr$_{0.7}$Ca$_{0.3}$CoO$_3$ is uniformly distributed over all sample volume,
despite the severe drop of moments. The ground state of these compounds is
identified with the LS/LS-related phase derived theoretically by Sboychakov
\textit{et al.} [Phys. Rev. B \textbf{80}, 024423 (2009)]. The ground state of
Nd$_{0.7}$Sr$_{0.3}$CoO$_3$ with an intermediate cobalt moment is inhomogeneous
due to competing of LS/LS and IS/LS phases. In the theoretical part of the
study, the crystal field split levels for $4f^3$ (Nd$^{3+}$), $4f^2$
(Pr$^{3+}$) and $4f^1$ (Ce$^{3+}$ or Pr$^{4+}$) are calculated and their
magnetic characteristics are presented.

Materials Science