Electric transport and magnetic properties of perovskites LaMn1-xCoxO3 up to 900 K

The structural, magnetic and transport properties of the LaMn1-xCoxO3 system were investigated over a wide, temperature range, 10-900 K. Two structural types, depending on x, were detected - orthorhombic Pbnm (x <= 0.5) and rhombohedral R3c (x > 0.6), separated by the bi-phasic sample x = 0.6. At both ends of the LaMn1-xCoxO3 system, the respective substituents are unambiguously characterized as Co2+ (x <= 0.1) and Mn4+ (x >= 0.9). On the Mn-rich side, up to x < 0.5, we infer on the basis of high temperature transport and magnetic data the gradual increase of the Co2+ valence towards the prevailing Co3+, while for the Co-rich samples (0.6 <= x <= 0.8), the Co3+ states tend to disproportionate at high temperatures to Co2+ + Co4+, which probably controls both the transport and magnetic properties. At low temperatures, the long range ferromagnetic order was confirmed by means of neutron diffraction for the x = 0.4 sample. A non-uniform magnetic state was detected at higher cobalt substitution up to x = 0.8 and was associated with FM clusters that are formed below similar to 220 K and coagulate below similar to 150 K.