Structural and magnetic studies of Sr2IrO4

The discovery of high-temperature superconductivity in doped copper oxides, which in their insulating forms are nearly ideal two-dimensional spin-1/2 Heisenberg antiferromagnets, has stimulated great interest in finding additional examples of such magnetic systems. We find that Sr2IrO4, which has the K2NiF4 structure and should have a 5d5 low-spin (S=1/2) electronic configuration, develops a ferromagnetic moment near 250 K. The small size of the remanent moment (10-2μB), and our structural studies, however, imply that this is weak ferromagnetism which appears at the Néel temperature due to a Dzyaloshinsky-Moriya interaction, in a manner analogous to that seen in La2CuO4.