Fincher-Burke excitations in the transverse spin-density-wave phase of chromium

High-resolution neutron-scattering measurements of the transversely polarized spin-density-wave phase of single-domain chromium are reported. The well-defined excitations observed by Fincher, Shirane, and Werner and later attributed to propagating modes by Burke et al. are characterized at energy transfers 0.75≤ΔE≤4 meV. These modes appear between the unresolved spin-wave peaks at ${\mathbf{Q}}_{\pm }$=${\mathit{a}}^{\mathrm{*}}$(1±δ,0,0) and follow a linear dispersion that originates at ${\mathbf{Q}}_{\pm }$. In contrast to previous measurements, no evidence of symmetric excitations at ‖q‖${\mathbf{Q}}_{\mathrm{-}}$‖ or ‖q‖>‖${\mathbf{Q}}_{+}$‖ is seen at any energy transfer. The absence of symmetric branches argues against a magnetovibrational interpretation of these modes. The susceptibility associated with these Fincher-Burke excitations is found to vary roughly as the inverse of the energy, 1/${\mathrm{\omega }}_{\mathrm{FB}}$.