Structural and magnetic properties of hexagonal perovskites La1.2Sr2.7MO7+d (M=Ru,Ir)

The structures of the new compound La1.2Sr2.7IrO7+d and the recently discovered La1.2Sr2.7RuO7+d have been solved using a combination of X-ray and neutron diffraction. Both compounds crystallize in the trigonal space group R-3m and contain isolated MO6 (M=Ru,Ir) octahedra, which are arranged in well-defined layers. Results of the magnetic susceptibility and XANES measurements show that the transition metal cations are in a pentavalent state. While in La1.2Sr2.7RuO7+d an antiferromagnetic interaction between the Ru5+ ions is found, La1.2Sr2.7IrO7+d shows a very small temperature-independent paramagnetism down to 1.8 K due to the strong spin-orbit coupling characteristic for the 5d element iridium.