The magnetic and crystal structures of Sr2IrO4: A neutron diffraction study

TL;DR

This neutron diffraction study elucidates the magnetic and crystal structures of Sr2IrO4, revealing a canted antiferromagnetic order with spin orientations tracking octahedral rotations and indicating reduced crystal symmetry.

Contribution

First detailed neutron diffraction analysis of Sr2IrO4's magnetic structure, showing spin canting and symmetry reduction, advancing understanding of its unconventional magnetism.

Findings

Long-range antiferromagnetic order with canted spins

Spin orientation tracks IrO6 octahedral rotation

Evidence of reduced crystal symmetry from forbidden reflections

Abstract

We report a single-crystal neutron diffraction study of the layered $\rm Sr_2IrO_4$. This work unambiguously determines the magnetic structure of the system and reveals that the spin orientation rigidly tracks the staggered rotation of the $\rm IrO_6$ octahedra in $\rm Sr_2IrO_4$. The long-range antiferromagnetic order has a canted spin configuration with an ordered moment of 0.208(3) $\mu_B$/Ir site within the basal plane; a detailed examination of the spin canting yields 0.202(3) and 0.049(2) $\mu_B$/site for the a axis and the b axis, respectively. It is intriguing that forbidden nuclear reflections of space group $I4_1/acd$ are also observed in a wide temperature range from 4 K to 600 K, which suggests a reduced crystal structure symmetry. This neutron-scattering work provides a direct, well-refined experimental characterization of the magnetic and crystal structures that are crucial to the understanding of the unconventional magnetism exhibited in this unusual magnetic insulator.