Structure and Magnetism of (La/Sr) 2 M 0.5 Ir V 0.5 O 4 and Topochemically Reduced (La/Sr) 2 M 0.5 Ir II 0.5 O 3 (M = Fe, Co) Complex Oxides.

Neutron powder diffraction data show that Sr2 Fe0.5 Ir0.5 O4 , Sr2 Co0.5 Ir0.5 O4 , and La0.5 Sr1.5 Co0.5 Ir0.5 O4 all adopt undistorted, n = 1 Ruddlesden-Popper structures in which the Ir5+ and Fe3+ /Co3+ /Co2+ cations are statistically disordered over all the octahedral coordination sites. Magnetization data indicate the two cobalt phases are spin glasses at low temperature, while Sr2 Fe0.5 Ir0.5 O4 appears to adopt an antiferromagnetic state with very small magnetically ordered domains. Topochemical reduction with a Zr getter converts the tetragonal A2 M0.5 Ir0.5 O4 phases to the corresponding orthorhombic A2 M0.5 Ir0.5 O3 phases in which the Ir2+ and Fe2+ /Co2+ /Co1+ cations are located in approximately square-planar coordination sites. Magnetization data indicate Sr2 Fe0.5 Ir0.5 O3 is a spin glass below TG ∼ 30 K, while Sr2 Co0.5 Ir0.5 O3 appears to be antiferromagnetic below TN ∼ 25 K and La0.5 Sr1.5 Co0.5 Ir0.5 O3 shows no sign of magnetic order for T > 5 K. The magnetic behavior of both the A2 M0.5 Ir0.5 O4 and A2 M0.5 Ir0.5 O3 phases is discussed on the basis of metal d-electron count and structural features.