Structure and Magnetism of (La/Sr)<sub>2</sub>M<sub>0.5</sub>Ir<sup>V</sup><sub>0.5</sub>O<sub>4</sub> and Topochemically\nReduced (La/Sr)<sub>2</sub>M<sub>0.5</sub>Ir<sup>II</sup><sub>0.5</sub>O<sub>3</sub> (M = Fe, Co) Complex Oxides
Jacob E. Page (6611645)Michael A. Hayward (1483720)
Abstract
Neutron powder diffraction data show\nthat Sr<sub>2</sub>Fe<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>4</sub>,\nSr<sub>2</sub>Co<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>4</sub>, and La<sub>0.5</sub>Sr<sub>1.5</sub>Co<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>4</sub> all adopt undistorted, <i>n</i> = 1 Ruddlesden–Popper\nstructures in which the Ir<sup>5+</sup> and Fe<sup>3+</sup>/Co<sup>3+</sup>/Co<sup>2+</sup> cations are statistically disordered over\nall the octahedral coordination sites. Magnetization data indicate\nthe two cobalt phases are spin glasses at low temperature, while Sr<sub>2</sub>Fe<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>4</sub> appears to adopt\nan antiferromagnetic state with very small magnetically ordered domains.\nTopochemical reduction with a Zr getter converts the tetragonal A<sub>2</sub>M<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>4</sub> phases to the\ncorresponding orthorhombic A<sub>2</sub>M<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>3</sub> phases in which the Ir<sup>2+</sup> and Fe<sup>2+</sup>/Co<sup>2+</sup>/Co<sup>1+</sup> cations are located in approximately\nsquare-planar coordination sites. Magnetization data indicate Sr<sub>2</sub>Fe<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>3</sub> is a spin glass\nbelow <i>T</i><sub>G</sub> ∼ 30 K, while Sr<sub>2</sub>Co<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>3</sub> appears to be antiferromagnetic\nbelow <i>T</i><sub>N</sub> ∼ 25 K and La<sub>0.5</sub>Sr<sub>1.5</sub>Co<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>3</sub> shows\nno sign of magnetic order for <i>T</i> > 5 K. The magnetic\nbehavior of both the A<sub>2</sub>M<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>4</sub> and A<sub>2</sub>M<sub>0.5</sub>Ir<sub>0.5</sub>O<sub>3</sub> phases is discussed on the basis of metal d-electron count and structural\nfeatures.
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