The magnetic and transport properties of the ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ system were studied at the characteristic points of the phase diagram corresponding to the ferromagnetic insulating and charge-ordered antiferromagnetic states. The magnetization M and resistivity $\rho$ of the ceramic samples with $x=0.2,$ 0.25, 0.27, 0.29, 0.30, and 0.33 were measured at temperatures $T=4\mathrm{}–300\mathrm{K}$ and applied magnetic fields H up to 7 T. It was shown that the Curie temperature $T_C$ exhibits a nonmonotonic change with x. The maximum value of $T_C$ was achieved at $x=\mathrm{0.25.}\mathrm{}$ The isotope substitution ${}^{16}{\overrightarrow{\mathrm{O}}}^{18}\mathrm{O}$ was performed for the samples with $x=0.2,0.25,$ and 0.30. A pronounced isotope effect in $T_C$ was found. A noticeable drop in the activation energy $E_a$ below the Curie temperature and a decrease of resistivity in the magnetic field both in the ferromagnetic insulator phase and in the phase-separated region at $x>\mathrm{}0.3\mathrm{}$ were observed. Special attention is paid to the possible manifestations of the phase separation in the ferromagnetic insulating state.

• Received 6 March 2003

DOI:https://doi.org/10.1103/PhysRevB.68.174403