Band structure and transport properties ofCrO2

Abstract

The local-spin-density approximation is used to calculate the energy bands of both the ferromagnetic and paramagnetic phases of metallic ${\mathrm{CrO}}_{2}$. The Fermi level lies in a peak in the paramagnetic density of states, and the ferromagnetic phase is more stable. As predicted by Schwarz, the Fermi level lies in an insulating gap in the minority-spin bands between oxygen p and chromium d states (``half-metallic'' behavior). The resulting magnetic moment is 2${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$ per Cr atom, in agreement with experiment. The ${\mathrm{A}}_{1\mathrm{g}}$ Raman frequency is predicted to be 587 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Drude plasma frequencies are of order 2 eV, as seen experimentally by Chase. The measured resistivity is used to find the electron mean free path \ensuremath{\ell}, which is only a few angstroms at 600 K, but, nevertheless, resistivity continues to rise as temperature increases. This puts ${\mathrm{CrO}}_{2}$ into the category of ``bad metals'' in common with the high-${\mathrm{T}}_{\mathrm{c}}$ superconductors, the high-T metallic phase of ${\mathrm{VO}}_{2}$, and the ferromagnet ${\mathrm{SrRuO}}_{3}$. In common with both ${\mathrm{SrRuO}}_{3}$ and ${\mathrm{Sr}}_{2}$${\mathrm{RuO}}_{4}$, the measured specific-heat parameter \ensuremath{\gamma} is higher than band theory predicts by a renormalization factor close to 4.