Interplay between transport, magnetic, and ordering phenomena in Sm1-xCaxMnO3

We present the detailed study of Sm1-xCaxMnO3 with 0.3 less than or equal to x less than or equal to 1 probed by electrical resistivity, thermoelectric power, magnetic susceptibility, and thermal conductivity measurements between 10 and 320 K. The transport and thermal data are analyzed supposing polaronic carriers and explanation of experimental results is made in coherence with ordering phenomena recently evidenced by electron diffraction and lattice imaging. Sample Sm0.7Ca0.3MnO3 an is insulating ferromagnet without any obvious transport anomalies at T(C)congruent to 95 K. Contrary to that, the compounds with 0.4 less than or equal to x less than or equal to 0.75 exhibit, at critical temperature T-crit, distinct anomalies in transport and magnetism. Respecting the recent electron microscopy results, these anomalies can be associated to the real space charge ordering of Mn3+/Mn4+ ions, i.e., T-crit=T-CO. Our experimental data indicate, however, that long-range antiferromagnetic order likely develops at T(N)similar to 130 K, i.e., well below T-CO. The Sm0.2Ca0.8MnO3 sample is a C-type antiferromagnet with p-type conductivity at low temperatures. For the samples with x similar to 0.9, the paramagnetic highly conducting state is replaced below T-crit=110 K by a "cluster glass" ferromagnetic state. The series is completed by a G-type CaMnO3 antiferromagnet with T-N=122 K. In all studied samples, the heat is conducted mainly by phonons with the mean free path critically limited in dependence of composition and temperature by scattering on impurities (Sm/Ca substitution), dynamic and/or static Jahn-Teller modes and spin fluctuations. Nevertheless, for the samples with 0.6 less than or equal to x less than or equal to 0.9, which exhibit high electrical resistivity in the paramagnetic state, the thermal conductivity at room temperature comprises significant electronic contribution. [S0163-1829(99)01744-0].