Magnetic Properties of the Fluorite-Related La3MO7 Phases, M=Ru and Os: Local Moment Magnetism, Short- and Local Moment Magnetisem,Short and Long-Range Order in 4d and 5d Transition Metal Oxides

The oxide materials La3MO7, M=Ru and Os have been prepared, the Os phase for the first time. Both crystallize in a fluoriterelated supercell with Cmcm symmetry with very similar lattice constants. A singular feature of this structure type is the presence of well- separated zig-zag chains of corner-sharing MO6 octahedra parallel to one of the orthorhombic axes. Local moment magnetic behavior is observed for both on very different energy scales. In each case the materials exhibit Curie–Weiss paramagnetism at high temperatures with effective moments consistent with S= , as expected for the 4d3 and 5d3 electronic configurations associated with oxidation state +5, thus providing evidence for local moment magnetism. At lower temperatures broad maxima occur near 20 K (Ru) and 110 K(Os) which can be attributed to intrachain magnetic correlations. Fits to an appropriate model yield Jintra/k values of -2.9 K for Ru and -23.2(1) K for Os. This ~eight-fold increase is attributed to the expanded radial extent of the d-orbitals in proceeding from the 4d to the 5d series. Evidence for long-range antiferromagnetic order is present in the form of sharp susceptibility maxima at 10 and 45 K for M=Ru and Os, respectively.