Anisotropic antiferromagnetic order in spin-orbit coupled trigonal lattice Ca2Sr2IrO6

TL;DR

This study reveals the magnetic structure and ordering of Ca2Sr2IrO6, showing anisotropic antiferromagnetic order with a specific wave vector, spin orientation, and a sizable magnetic moment, supported by experimental and theoretical analysis.

Contribution

The paper provides the first detailed determination of the magnetic structure of Ca2Sr2IrO6, highlighting its anisotropic antiferromagnetic order and the influence of magnetic fields, supported by neutron diffraction and density functional theory.

Findings

Long-range antiferromagnetic order below 13.1 K.

Magnetic wave vector identified as (0,0.5,1).

Ordered magnetic moment of 0.66 μB per Ir.

Abstract

We used single-crystal x-ray and neutron diffraction to investigate the crystal and magnetic structures of trigonal lattice iridate Ca2Sr2IrO6. The crystal structure is determined to be $R\bar3$ 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$^\circ$ towards 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 $\rm IrO_6$ octahedral networks. The tilting angle is reduced to $\approx19^\circ$ when a magnetic field of 4.9 Tesla 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 $\sim0.5$~eV.