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 temperatu re 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 antiferrom agnetic charge-ordered insulator (AFCO) can be switched to the ferromagneti c metallic state (FMM) by application of a relatively weak external magneti c field. This is accompanied by a huge CMR effect, irreversible at low temp eratures. The neutron diffraction data, which show a decoupling of charge o rder (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 co nfirmed the transformation of the x = 0.2 sample to FMM state and the natur e of the AFCO-FMM transition was probed by magnetic moment and electrical r esistivity relaxation measurements. This comprehensive characterization of the sample led to a complete determination of the magnetic phase diagram wh ich demonstrated the near degeneracy of the ferro- and antiferromagnetic gr ound states in Pr0.8Na0.2MnO3. (C) 2001 American Institute of Physics.