Incommensurate magnetic correlations in ${\mathrm{La}}_{1.8}$${\mathrm{Sr}}_{0.2}$${\mathrm{NiO}}_4$

Neutron scattering experiments on an insulating single crystal of ${\mathrm{La}}_{1.8}$ ${\mathrm{Sr}}_{0.2}$ ${\mathrm{NiO}}_4$ show the presence of strong two-dimensional incommensurate magnetic correlations in the ${\mathrm{NiO}}_2$ planes. At low temperatures, T=2 K, these exist on time scales τ>${10}^{\mathrm{-}11}$ s. The typical side length of the correlated regions in the direction parallel to the incommensurate modulation is equal to the average spacing between strontium atoms.