Structural and magnetic studies of ${\mathrm{Sr}}_2$${\mathrm{IrO}}_4$

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{-}2}$${\mathrm{\mu }}_{\mathit{B}}$), and our structural studies, however, imply that this is weak ferromagnetism which appears at the Néel temperature due to a Dzyaloshinsky-Moriya interaction, in a manner analogous to that seen in ${\mathrm{La}}_2$${\mathrm{CuO}}_4$.