Robustness of basal-plane antiferromagnetic order and the $J_{eff}=1/2$   state in single-layer iridate spin-orbit Mott insulators
  The magnetic structure and electronic groundstate of the layered perovskite Ba2IrO4 have been investigated using x-ray resonant magnetic scattering (XRMS). Our results are compared with those for Sr2IrO4, 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 groundstate in Ba2IrO4, deduced from an investigation of the XRMS $L_3/L_2$ intensity ratio, is consistent with a $J_{eff}=1/2$ 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. 
S. Boseggia, R. Springell, H. C. Walker, Ch. R\"uegg, H. Okabe, M.   Isobe, R. S. Perry, S. P. Collins and D. F. McMorrow
cond-mat.str-el