Measurement of the internal magnetic field in the correlated iridates Ca4IrO6, Ca5Ir3O12, Sr3Ir2O7 and Sr2IrO4.

Oxides containing iridium ions display a range of magnetic and conducting properties that depend on the delicate balance between interactions and are controlled, at least in part, by the details of the crystal architecture. We have used muon spin rotation (μSR) to study the local field in four iridium oxides, Ca4IrO6, Ca5Ir3O12, Sr3Ir2O7, and Sr2IrO4, which show contrasting behavior. Our μSR data on Ca4IrO6 and Ca5Ir3O12 are consistent with conventional antiferromagnetism where quasistatic magnetic order develops below TN=13.85(6) and 7.84(7) K, respectively. A lower internal field is observed for Ca5Ir3O12, as compared to Ca4IrO6, reflecting the presence of both Ir4+ and Ir5+ ions and resulting in a more magnetically dilute structure. Muon precession is only observed over a restricted range of temperature in Sr3Ir2O7, while the Mott insulator Sr2IrO4 displays more complex behavior, with the μSR signal containing a single, well-resolved precession signal below TN=230 K, which splits into two precession signals at low temperature following a reorientation of the spins in the ordered state. [ABSTRACT FROM AUTHOR]