UC Berkeley

We report the structural and magnetic ground state properties of the monoclinic compound barium iridium oxide Ba4Ir3O10 using a combination of resonant x-ray scattering, magnetometry, and thermodynamic techniques. Magnetic susceptibility exhibits a pronounced antiferromagnetic transition at TN≈25 K, a weaker anomaly at TS≈142 K, and strong magnetic anisotropy at all temperatures. Resonant elastic x-ray scattering experiments reveal a second order structural phase transition at TS and a magnetic transition at TN. Both structural and magnetic superlattice peaks are observed at L = half integer values. The magnetization anomaly at TS implies the presence of magnetoelastic coupling, which conceivably facilitates the symmetry lowering. Mean field critical scattering is observed above TS. The magnetic structure of the antiferromagnetic ground state is discussed based on the measured magnetic superlattice peak intensity. Our study not only presents essential information for understanding the intertwined structural and magnetic properties in Ba4Ir3O10 but also highlights the necessary ingredients for exploring novel ground states with octahedra trimers.