Orbital character of $\mathrm{O}-2p$ unoccupied states near the Fermi level in ${\mathrm{CrO}}_2$

The orbital character, orientation, and magnetic polarization of the $\mathrm{O}-2p$ unoccupied states near the Fermi level ${(E}_F)$ in ${\mathrm{CrO}}_2$ was determined using polarization-dependent x-ray absorption spectroscopy and x-ray magnetic circular dichroism from high-quality, single-crystal films. A sharp peak observed just above $E_F$ is excited only by the electric-field vector $\left(\mathbf{E}\right)$ normal to the tetragonal c axis, characteristic of a narrow band $(\approx 0.7$ eV bandwidth) constituted from $\mathrm{O}-2p$ orbitals perpendicular to c $(\mathrm{O}-{2p}_y)$ hybridized with Cr ${3d}_{\mathrm{xz}-\mathrm{yz}}{t}_{2g}$ states. By comparison with band-structure and configuration-interaction cluster calculations our results support a model of ${\mathrm{CrO}}_2$ as a half-metallic ferromagnet with large exchange-splitting energy $\left({\Delta }_{\mathrm{exch}-\mathrm{split}}\approx 3.0\mathrm{eV}\right)$ and substantial correlation effects.