New Insulating Antiferromagnetic Quaternary Iridates MLa(10)Ir(4)O(24) (M = Sr, Ba)

Recently, oxides of Ir(4+) 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) = ½, that defines the electronic and magnetic properties. The canonical example is the Ruddlesden-Popper compound Sr(2)IrO(4), which has been suggested as a potential route to a new class of high temperature superconductor due to the formal analogy between J(eff) = ½ and the S = ½ 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, MLa(10)Ir(4)O(24) (M = Sr, Ba). The crystal structure of both compounds features isolated IrO(6) octahedra in which the electronic configuration of Ir is d(5). Both compounds order antiferromagnetically despite the lack of obvious superexchange pathways, and resistivity measurement shows that SrLa(10)Ir(4)O(24) is an insulator.