Crystal and magnetic study of the disordered perovskites Ca(Mn0.5Sb0.5)O3 and Ca(Fe0.5Sb0.5)O3

We have investigated the double perovskites Ca2MSbO6 (M = Mn, Fe) that have been prepared by solid-state reaction (M = Fe) and wet chemistry procedures (M = Mn). The crystal and magnetic structures have been studied from X-ray (XRD) and neutron powder diffraction (NPD) data. Rietveld refinements show that the crystal structures are orthorhombic (space group Pbnm) with complete disorder of M and Sb cations, so the formula should be rewritten as Ca(M0.5Sb0.5)O3. Due to this disorder no evidences of Jahn–Teller distortion can be observed in the MnO6 octahedra of Ca(Mn0.5Sb0.5)O3, in contrast with the ordered double perovskite Sr2MnSbO6. Ca(Fe0.5Sb0.5)O3 behaves as an antiferromagnet with an ordered magnetic moment for Fe3+ of 1.53(4)μB and a propagation vector k = 0, as investigated by low-temperature NPD. The antiferromagnetic ordering is a result of the high degree of Fe/Sb anti-site disorder of the sample, which originates the spontaneous formation of Fe-rich islands, characterized by the presence of strong Fe–O–Fe antiferromagnetic couplings with enough long-range coherence to produce a magnetic contribution perceptible by NPD. By contrast, the magnetic structure of Ca(Mn0.5Sb0.5)O3 cannot be observed by low-temperature NPD because the magnitude of the ordered magnetic moments is below the detection threshold for neutrons.