Ba2IrO4: A spin-orbit Mott insulating quasi-two-dimensional antiferromagnet

A layered iridate Ba2IrO4 was synthesized using a high-pressure synthesis technique. Its electronic state was studied through electrical resistivity, magnetic susceptibility, and mu SR experiments. It was found that Ba2IrO4 crystallizes in a K2NiF4-type structure (space group I4/mmm) with lattice parameters a = 4.030(1) angstrom and c = 13.333(4) angstrom. The structure includes flat IrO2 square planar lattices with straight Ir-O-Ir bonds. Ba2IrO4 is a Mott insulator (activation energy Delta E-a similar to 0.07 eV) driven by a spin-orbit interaction. The magnetic susceptibility and mu SR studies revealed that the magnetic ground state is antiferromagnetic long-range order (T-N similar to 240 K) in which the magnetic moment (similar to 0.34 mu(B)/Ir atom) is significantly reduced by a low-dimensional quantum spin fluctuation with a large intraplane correlation vertical bar J vertical bar. The behavior is similar to that in parent materials of high-T-C cuprate superconductors such as La2CuO4.