Reflectivity spectra of Eu rich EuO near the absorption edge

Abstract

The reflectivity spectra at near normal incidence in the spectral range 1.5 μm to 4 μm of EuO single crystals slightly rich in Eu but almost stoichiometric have been measured in the temperature range 4.2 to 300 K, using the Voigt configuration. Two dips are observed at 1.85 and 2.20 μm in fairly good agreement with the location of the two absorption peaks observed in similar materials. These peaks are ascribed in the literature either to optical transitions of an electron bound to an oxygen vacancy or to transitions into F centres formed at the vacancies. Our measurements show a very small temperature dependence of the energy position of the dips in the whole range [4.2-300 K] and a small intensity of the dips, which is in favour of the first interpretation when the material is an insulator, and of an alternative one in the metallic configuration, i.e. an interband transition between up and down spin subbands. At 4.2 K, two extra dips appear at 1.74 and 2 μm. The magnetic field up to 30 kG does not affect the energy position of the different dips, but greatly affects their shape.