High-pressure syntheses, crystal structures, and magnetic properties of novel quadruple perovskite oxides LaMn3Ru2Mn2O12 and LaMn3Ru2Fe2O12

Quadruple perovskite oxides LaMn ₃Ru ₂ M ₂O ₁₂ ( M = Mn, Fe) have been synthesized under high-pressure and high-temperature conditions of 8 GPa and 1373 K. Synchrotron X-ray powder diffraction study demonstrates that both oxides crystallized in AA` <sub>3</sub> B <sub>4</sub>O <sub>12</sub> -type cubic quadruple perovskite structures, where the Ru and M ions did not form the special ordering at B -site. X-ray absorption spectroscopy reveals that the valence states are represented as LaMn <sup>3+</sup> <sub>3</sub>Ru <sup>3+</sup> <sub>2</sub> M <sup>3+</sup> <sub>2</sub>O <sub>12</sub> ( M = Mn, Fe) in the ionic models, indicating that the isovalent states of Ru <sup>3+</sup> and M <sup>3+</sup> ions disturb the B -site ordering. Magnetization, heat capacity, and neutron diffraction data prove that short-range magnetic orderings are predominant for both compounds instead of long-range magnetic orderings. We conclude that the competition between ferromagnetic and antiferromagnetic superexchange interactions between Ru <sup>3+</sup> and M <sup>3+</sup> ions at B-site prevent the long-range magnetic ordering Mn <sup>3+</sup> ions at A′-site, although the A`- and B-site magnetic sublattices are expected to be intrinsically independent in A′-Mn quadruple perovskite system. This finding represents that the atomic ordering of the B-site is essential for the precise design of magnetic structures for the LaMn ₃ M ₂ M′ ₂O ₁₂ quadruple perovskite series.