Raman spectroscopy of ferromagnetic CrO₂

Polarized Raman spectra of the ferromagnetic metal CrO₂ were measured in a broad temperature range including T_c≈390K. The Raman-allowed modes of A_1g, B_1g, B_2g, and E_g symmetry were identified and compared to the corresponding modes of isostructural TiO₂. The two low-frequency Raman lines are relatively narrow, indicating weak scattering of the corresponding B_1g and E_g phonons. Whereas the Raman intensities are not visibly affected by the magnetic ordering, the dependences on temperature of the phonon wave numbers exhibit peculiarities that could be attributed to a spin-phonon interaction. The variations with T of the phonon linewidths follow at low temperatures the dependence expected for phonon-phonon scattering. An additional broadening at higher temperatures with a maximum near T_c is tentatively assigned to scattering from collective spin fluctuations.