Structural and Magnetic Transitions in the Planar Antiferromagnet Ba$_4$Ir$_3$O$_{10}$

TL;DR

This study investigates the structural and magnetic phase transitions in Ba$_4$Ir$_3$O$_{10}$, revealing a second order structural transition and antiferromagnetic ordering, with evidence of magneto-elastic coupling and complex magnetic structure.

Contribution

It provides detailed experimental insights into the intertwined structural and magnetic transitions in Ba$_4$Ir$_3$O$_{10}$, highlighting the role of magneto-elastic coupling and superlattice peaks.

Findings

Structural phase transition at T_S ≈ 142K

Antiferromagnetic transition at T_N ≈ 25K

Presence of magneto-elastic coupling

Abstract

We report the structural and magnetic ground state properties of the monoclinic compound barium iridium oxide Ba$_4$Ir$_3$O$_{10}$ using a combination of resonant x-ray scattering, magnetometry, and thermodynamic techniques. Magnetic susceptibility exhibits a pronounced antiferromagnetic transition at $T_{\text{N}}$ $\approx$ 25K, a weaker anomaly at $T_{\text{S}}$ $\approx$ 142K, and strong magnetic anisotropy at all temperatures. Resonant elastic x-ray scattering experiments reveal a second order structural phase transition at $T_{\text{S}}$ and a magnetic transition at $T_{\text{N}}$. Both structural and magnetic superlattice peaks are observed at $L$ = half integer values. The magnetization anomaly at $T_{\text{S}}$ implies the presence of magneto-elastic coupling, which conceivably facilitates the symmetry lowering. Mean field critical scattering is observed above $T_{\text{S}}$. 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 Ba$_4$Ir$_3$O$_{10}$, but also highlights the necessary ingredients for exploring novel ground states with octahedra trimers.