Abstract
We report a single-crystal neutron diffraction study of the layered Sr2IrO4. This work unambigu-
ously determines the magnetic and crystal structures, and reveals that the spin orientation rigidly
tracks the staggered rotation of the IrO6 octahedra in Sr2IrO4. The long-range antiferromagnetic
order has a canted spin configuration with an ordered moment of 0.208(3) μB/Ir site within the
basal plane; a detailed examination of the spin canting yields 0.202(3) and 0.049(2) μB/site for the
a-axis and the b-axis, respectively. It is intriguing that forbidden nuclear reflections of space group
I41/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 experimen-
tal characterization of the magnetic and crystal structures that are crucial to the understanding of
the unconventional magnetism existent in this unusual magnetic insulator.
