Magnetic phase diagrams of L1-xAxMnO3 manganites (L = Pr,Sm; A = Ca,Sr)

The magnetic phase diagrams of four L(1-x)A(x)MnO(3) series (L=Pr,Sm; A = Ca,Sr) have been established combining neutron diffraction, electron microscopy, and magnetotransport measurements in order to understand and optimize the colossal magnetoresistance (CMR) properties of these compounds. A complementary study of the La1-xCaxMnO3 phase diagram (x greater than or equal to 0.8) is also performed. The comparison of these diagrams demonstrates that low [r(A)] values are required to obtain CMR properties on the Mn4+ rich side, i.e., when a competition between charge order and cluster glass phases occurs (L1-xCaxMnO3; L= Pr,Sm), As a consequence of the low [r(A)] values on the rich Mn3+ side (x<0.5 in L1-xCaxMnO3), the ferromagnetic metallic (FMM) state is never reached, whereas for the same x values, systems with larger [r(A)] (L1-xSrxMnO3; L = Pr,Sm) exhibit CMR properties related to the FMM state. A particular attention is paid to the x similar to 0.5 compositions of these L1-xSrxMnO3 series for which the Curie and Neel temperatures are T-N<T-C and T-C <T-N for Pr and Sm, respectively. The importance of the chemical factors on the charge ordering (studied vs temperature by electron diffraction) and on the magnetic structures (from neutron diffraction) is also emphasized. [S0163-1829(99)11241-4].