Temperature-dependence of the lattice dynamics of Cr across its magnetic transitions

Chromium is a classic spin-density-wave system. Its phonon dispersion relations at room temperature show a number of anomalies, which can be related to the details of the spin-dependent electronic structure. As the temperature is varied, Cr undergoes two magnetic transitions, one at 311 K, and the other at 123 K, and the elastic constants are known to change abruptly across these transitions. Thus far, there has been very limited information about the behavior of the phonon dispersion relations across these transitions, but large changes appear likely. We have employed high-resolution inelastic x-ray scattering to address this question. The experiment was carried out at Sector 3 of the Advanced Photon Source. Surprisingly, we have found no obvious abrupt changes in the phonon dispersion relations across the magnetic transitions. The phonon frequencies remain largely the same for sample temperatures down to 30 K.