Reinvestigation of magnetic excitations in the spin density wave of chromium

Low-energy magnetic excitations of chromium have been reinvestigated with a single-${\mathit{Q}}_{\ifmmode\pm\else\textpm\fi{}}$ crystal using neutron scattering techniques. In the transverse spin-density-wave phase a well-defined magnetic excitation is found around $(0,0,1)$ with a weak dispersion perpendicular to the wave vector of the incommensurate structure. The magnetic excitation has an energy gap of $\ensuremath{\omega}\ensuremath{\simeq}4\mathrm{meV}$ at $(0,0,1),$ which exactly corresponds to the Fincher excitation previously studied only along the incommensurate wave vector.