New insulating antiferromagnetic quaternary iridates MLa₁₀Ir₄O₂₄ (M=Sr, Ba)

Recently, oxides of Ir⁴⁺ have received renewed attention in the condensed matter physics community, as it has been reported that certain iridates have a strongly spin-orbital coupled (SOC) electronic state, J_eff =1/2, that defines the electronic and magnetic properties. The canonical example is the Ruddlesden-Popper compound Sr₂IrO₄, which has been suggested as a potential route to a new class of high temperature superconductor due to the formal analogy between J_eff=1/2 and the S=1/2 state of the cuprate superconductors. The quest for other iridium oxides that present tests of the underlying SOC physics is underway. In this spirit, here we report the synthesis and physical properties of two new quaternary tetravalent iridates, MLa₁₀Ir₄O₂₄ (M=Sr, Ba). The crystal structure of both compounds features isolated IrO₆ octahedra in which the electronic configuration of Ir is d⁵. Both compounds order antiferromagnetically despite the lack of obvious superexchange pathways, and resistivity measurement shows that SrLa₁₀Ir₄O₂₄ is an insulator.