Magnetic and crystal structures of Sr sub(2) IrO sub(4): A neutron diffraction study

We report a single-crystal neutron diffraction study of the layered Sr sub(2) IrO sub(4). This work unambiguously determines the magnetic structure of the system and reveals that the spin orientation rigidly tracks the staggered rotation of the IrO sub(6) octahedra in Sr sub(2) IrO sub(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 sub(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.