Magnetically Ordered Perovskites in the System La1−xCaxFe1− xMnxO3

A series of solid solutions with the general formula La1−xCaxFe1− xMnxO3, where x is from 0.0 to 1.0, have been synthesized and their structural, magnetic and electrical properties have been studied. Polycrystalline samples were prepared by the usual ceramic method, firing at 1350° under a flow of oxygen gas to keep the cations in the desired valence states. X-ray diffraction shows these samples to be orthorhombically distorted perovskites for compositions up to x=0.3 and apparently cubic perovskites from 0.3<x<0.7. Beyond this composition two phases are present. From the measurements of magnetization between liquid-nitrogen and room temperatures, there appeared no evidence of ferromagnetic couplings between cations in the B sites as expected from the Goodenough and Kanamori rules, but they showed very weak residual magnetic moment (around 0.04 μB per formula unit). Mössbauer spectra showed that the iron ions stay in the trivalent state. Chemical analysis shows that at least 97% of the Mn is present as Mn4+. Electrical resistivity and thermo-emf measurements indicate that conduction in these samples apparently occurs by a hopping mechanism.