Anisotropic Antiferromagnetic Order In The Spin-orbit Coupled Trigonal-lattice Ca2sr2iro6

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 (3) over bar 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 degrees toward the c axis. The ordered moment is 0.66(3) mu(B) /Tr, larger than other iridates where iridium ions form corner- or edge-sharing IrO6 octahedral networks. The tilting angle is reduced to approximate to 19 degrees 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 similar to 0.5 eV.