Cationic ordering and role of the B-site lanthanide(III) and molybdenum(V) cations on the structure and magnetism of double perovskites Sr₂LnMoO₆

Highlights: • Five new double perovskites of formula Sr₂LnMoO₆ were synthesized. • All the samples crystallize in the monoclinic P2₁/n space group. • Strong reducing conditions were used in order to stabilized Mo(V) cations. • A complete ordering between the rare earth and molybdenum ions was observed. • Magnetism agrees with the crystal distortions observed from Rietveld analysis. - Abstract: We describe the preparation, crystal structure determination and magnetic properties of a new series of ordered double perovskite oxides Sr₂LnMoO₆ (Ln = Eu, Gd, Dy, Ho, Er, Yb) with Mo⁵⁺ and Ln³⁺ electronic configurations. These compounds have been obtained by solid state reaction under reducing conditions in order to stabilize Mo⁵⁺ cations. Structural characterization by XRPD and NPD was performed when Ln = Ho, Er, Yb and just XRPD for absorbing Ln = Eu, Gd, Dy. At room temperature, an excellent Rietveld fit was obtained for all the samples in a monoclinic symmetry, space group P2₁/n, with long-range ordering of Ln and Mo atoms. Magnetic susceptibility measurements show that some of these materials present magnetic ordering below 25 K and the determined effective magnetic moments are consistent with those expected for the pair Ln³⁺–Mo⁵⁺. All the phases have negative valuesof the Weiss temperature indicating dominance of antiferromagnetic interactions