Magnetic and elastic properties of La sub 2 NiO sub 4+ x

We present experimental data on elastic constants, magnetic susceptibility, and magnetization for single-crystal La{sub 2}NiO{sub 4}. Strong acoustic anomalies especially for the {ital c}{sub 66} mode are observed for the structural tetragonal-orthorhombic transition at 360 K, whereas for the lower structural transition at 80 K the acoustic effects are rather smeared out. With the help of our magnetic measurements, we can construct a spin model describing the essential features of the magnetic structure in La{sub 2}NiO{sub 4}.