Ellipsometric study of the electronic band structure of CrO2 across the ferromagnetic transition

The optical properties of half-metallic CrO2 at temperatures below, at, and above the Curie temperature are studied by means of variable angle spectroscopic ellipsometry. The films were epitaxially grown on (100)- and (110)-oriented TiO2 substrates by chemical vapor deposition. Optical conductivity data reveal a pronounced anisotropy of the optical constants for all films which is in good agreement with what is known about their crystal structure. The main features of the conductivity spectra in the ferromagnetic state are consistent with existing band-structure calculations. However, no temperature dependence of these features across the ferromagnetic transition is evident, posing questions about the electronic structure of the material.