Structural and magnetic properties in a planar antiferromagnet

A monoclinic compound barium iridium oxide was proposed to host exotic magnetic ground states. By using a combination of thermodynamic, magnetometry and resonant x-ray scattering techniques, we report the structural and magnetic properties of this momoclinic compound. The magnetization data indicates a pronounced antiferromagnetic transition at 25K, a weaker anomaly at 142K, and strong magnetic anisotropy at all temperatures. Resonant elastic x-ray scattering experiments reveal a second order structural phase transition at Ts~142K and a magnetic transition at Tn~25K. Both structural and magnetic superlattice peaks are observed. Magneto-elastic coupling might facilitate the symmetry lowering at Ts, which induces the magnetic anomaly in the magnetization data. Furthermore, our scaling analysis suggests the mean-field like structure transition at Ts. The magnetic ground state below Tn is discussed based on the measured magnetic superlattice peak intensity. Our study presents valuable information for understanding the structural and magnetic properties in this new barium iridium oxides.