Structural effects in R0.5Sr0.5MnO3 perovskites (R = rare earth)

A comprehensive magnetic phase diagram for the perovskites R0.5Sr0.5MnO3 (R = trivalent rare-earth ions) that show an antiferromagnetic (AFM) transition at low temperature, and an A-type layered AFM structure is constructed by using the global instability index, R1, as a structural parameter. The phase boundaries are well defined in the phase diagram, indicating that R1 is an adequate structural parameter for depicting the structural effects arising from both the cation disorder and size mismatch on the magnetic and electric properties of the perovskite manganites. It is shown that variation of the antiferromagnetic transition temperature, TN, that occurs upon R3+ substitution is different to that on Sr2+ substitution; this can be understood in terms of a tuned competition between ferromagnetic and antiferromagnetic interactions. On the basis of bond valence analysis, a neutron diffraction experiment and the transport properties, we propose a novel approach of classifying two types of R0.5A'0.5MnO3 compound (A' = divalent alkaline-earth ions) according to the magnetic structure, and accordingly the resistivity, of the ground state of a compound. Such a classification reveals a close correlation among the magnetic, crystal structure and transport properties of the compounds. The electronic effects in these two types of compound seem to be different in magnitude and lead to different AFM structures. (author)