Structure and magnetic properties of ${\mathrm{Sr}}_{2\mathrm{-}\mathit{x}}$${\mathit{A}}_{\mathit{x}}$${\mathrm{IrO}}_4$ (A=Ca and Ba)

The effects of Ca and Ba substitutions for Sr on the structure and properties of ${\mathrm{Sr}}_2$${\mathrm{IrO}}_4$ were studied. Increase in the Ir-O(2)-Ir bond angle in the ${\mathrm{IrO}}_2$ plane was found after the substitutions of Ca and Ba for Sr. However, the Ir-O(2) distance is found to be unchanged by the Ba substitution, while it decreases by the Ca substitution. Regardless of these structural changes, the magnetic transition temperature at 240 K was found to be unchanged. Semiconductive behavior of the resistivity was found for all compounds with the increase in activation energy above 200 K. Both the electrical resistivity and the Seebeck coefficient showed no remarkable anomaly around the magnetic transition temperature.