Strain wave in pure chromium

New satellites were observed in a single crystal of pure chromium below the Néel point by X-ray diffraction at the positions apart by 2δ from the Bragg points. The observed anisotropy of the satellite intensity around the Bragg point and the temperature dependence of 2δ yield the conclusion that the lattice spacing in the direction of the wave vector of the spin density wave are modulated periodically and that the period is a half of that of the SDW. The experimental results coincide with the prediction made by a theory of the exchange striction in transition metal alloys.