Dependence of the E₁ reflectivity structure in EuO on temperature and doping

The temperature dependence of the E1 reflectivity peak (4f 7→4f65d transition) in both intrinsic and Gd-doped single crystal EuO over the range 20°-300°K has been measured. It is observed that this structure occurs consistently at lower energies in Gd-doped EuO vis-a-vis intrinsic for all temperatures covered. X-ray data indicate a smaller lattice constant for the doped material thus substantiating the direction of the shift on the basis of an overlap model. A strong Burstein-Moss effect would have shifted the peak oppositely to that observed. The onset of the "red shift" associated with magnetic ordering in the bulk occurs at a higher temperature for the doped material consistent with its higher T c, but the shift is not as closely correlated with this temperature as it is for intrinsic EuO. These results suggest a localized model for the E1 excitation. © 1971 The American Institute of Physics.