Yang, L.Jeong, M.Arakcheeva, A.Zivkovic, I.Náfrádi, B.Magrez, A.Pisoni, A.Jacimovic, J.Katukuri, V. M.Katrych, S.Shaik, N. E.Yazyev, O. V.Forro, L.Rønnow, Henrik M.2016-10-182016-10-182016-10-18201610.1103/PhysRevB.94.104403https://infoscience.epfl.ch/handle/20.500.14299/130231WOS:000383231600004We report the synthesis of single crystals of a novel layered iridate Ba21Ir9O43 and present the crystallographic, transport, and magnetic properties of this material. The compound has a hexagonal structure with two iridium oxide layers stacked along the c direction. One layer consists of a triangular arrangement of Ir2O9 dimers while the other layer comprises two regular octahedra and one triangular pyramid, forming interpenetrated triangular lattices. The resistivity as a function of temperature exhibits an insulating behavior, with a peculiar T-3 behavior. Magnetic susceptibility shows antiferromagnetic Curie-Weiss behavior with Theta(CW) similar or equal to -90 K while a magnetic transition occurs at a substantially lower temperature of 9 K. We discuss possible valence states and effective magnetic moments on Ir ions in different local environments and argue that the Ir ions in a unique triangular-pyramidal configuration likely carry unusually large magnetic moments.text::journal::journal article::research article