Magnetic phase diagram of the charge ordered manganite Pr0.8Na0.2MnO3

Pr1-xNaxMnO3 solid solutions up to x = 0.25 were prepared. Irrespective of magnetic order all samples are electrically insulating. The Curie temperature is maximum at T-C = 125 K for x = 0.15; the samples with x greater than or equal to 0.2 are charge-ordered antiferromagnets. The x = 0.2 antiferromagnetic charge-ordered insulator (AFCO) can be switched to the ferromagnetic metallic state (FMM) by application of a relatively weak external magnetic field. This is accompanied by a huge CMR effect, irreversible at low temperatures. The neutron diffraction data, which show a decoupling of charge order (T-CO = 215 K) and long range AF order of the "pseudo" CE (T-N = 175 K), are supported by specific heat measurement. The specific heat at 14 T confirmed the transformation of the x = 0.2 sample to FMM state and the nature of the AFCO-FMM transition was probed by magnetic moment and electrical resistivity relaxation measurements. This comprehensive characterization of the sample led to a complete determination of the magnetic phase diagram which demonstrated the near degeneracy of the ferro- and antiferromagnetic ground states in Pr0.8Na0.2MnO3. (C) 2001 American Institute of Physics.