SR2RHO4 AND SR2IRO4 - STRUCTURAL AND MAGNETIC STUDIES OF 4D AND 5D TRANSITION-METAL ANALOGS OF LA2CUO4

X-ray and neutron diffraction studies of Sr2IrO4 and Sr2RhO4 reveal st ructural distortions from the ideal K2NiF4 structure, in which the IrO 6 and RhO6 octahedra are rotated about the crystallographic c-axes by 11 degrees or 9.7 degrees, respectively. These rotations reduce the sy mmetry from I4/mmm to I4(1)/acd. We find that Sr2IrO4 is an electrical insulator which exhibits weak ferromagnetism at 250 K, attributable t o canted antiferromagnetism associated with long-range three-dimension al ordering of the Ir4+ moments. Although no ferromagnetic ordering is found in Sr2RhO4, susceptibility data shows a peak possibly associate d with two-dimensional short-range antiferromagnetic order. Doping of electrons in Sr2RhO4 results in compositions which show weak ferromagn etism, perhaps arising from double-exchange-type magnetic interactions due to the presence of rhodium in 4(+) and 3(+) oxidation states.