Robustness of Basal-Plane Antiferromagnetic Order and theJeff=1/2State in Single-Layer Iridate Spin-Orbit Mott Insulators

The magnetic structure and electronic ground state of the layered perovskite ${\mathrm{Ba}}_2{\mathrm{IrO}}_4$ have been investigated using x-ray resonant magnetic scattering. Our results are compared with those for ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$, for which we provide supplementary data on its magnetic structure. We find that the dominant, long-range antiferromagnetic order is remarkably similar in the two compounds and that the electronic ground state in ${\mathrm{Ba}}_2{\mathrm{IrO}}_4$, deduced from an investigation of the x-ray resonant magnetic scattering $L_3/L_2$ intensity ratio, is consistent with a $J_{\mathrm{eff}}=1/2$ description. The robustness of these two key electronic properties to the considerable structural differences between the Ba and Sr analogues is discussed in terms of the enhanced role of the spin-orbit interaction in $5d$ transition metal oxides.