Structural and magnetic studies ofSr2IrO4

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 ${\mathrm{Sr}}_{2}$${\mathrm{IrO}}_{4}$, which has the ${\mathrm{K}}_{2}$${\mathrm{NiF}}_{4}$ structure and should have a 5${\mathit{d}}^{5}$ low-spin (S=1/2) electronic configuration, develops a ferromagnetic moment near 250 K. The small size of the remanent moment (${10}^{\mathrm{\ensuremath{-}}2}$${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$), and our structural studies, however, imply that this is weak ferromagnetism which appears at the N\'eel temperature due to a Dzyaloshinsky-Moriya interaction, in a manner analogous to that seen in ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4}$.