We used single-crystal x-ray and neutron diffraction to investigate the crystal and magnetic structures of trigonal lattice iridate ${\mathrm{Ca}}_2{\mathrm{Sr}}_2{\mathrm{IrO}}_6$. The crystal structure is determined to be $R\overline{3}$ with two distinct Ir sites. The system exhibits long-range antiferromagnetic order below $T_N=13.1$ K. The magnetic wave vector is identified as (0,0.5,1) with ferromagnetic coupling along the $a$ axis and antiferromagnetic correlation along the $b$ axis. Spins align dominantly within the basal plane along the [1,2,0] direction and tilt ${34}^{\circ }$ toward the $c$ axis. The ordered moment is 0.66(3) ${\mu }_B$/Ir, larger than other iridates where iridium ions form corner- or edge-sharing ${\mathrm{IrO}}_6$ octahedral networks. The tilting angle is reduced to $\approx {19}^{\circ }$ when a magnetic field of 4.9 T is applied along the $c$ axis. Density functional theory calculations confirm that the experimentally determined magnetic configuration is the most probable ground state with an insulating gap $\sim 0.5$ eV.

• Received 15 March 2018
• Revised 5 May 2018

DOI:https://doi.org/10.1103/PhysRevB.97.235116