Phase separation and isotope effect in the ferromagnetic insulating state of the Pr1-xCaxMnO3 system (0.2<x<0.33) -: art. no. 174403

The magnetic and transport properties of the Pr1-xCaxMnO3 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=4-300 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=0.25. The isotope substitution O-16-->O-18 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>0.3 were observed. Special attention is paid to the possible manifestations of the phase separation in the ferromagnetic insulating state.