The frequency dependence of the real ε1(ω) and imaginary ε2(ω) parts of the complex dielectric permittivity of Co2NbAl and Co2VAl Heusler alloys has been investigated in the energy range of 0.15–5 eV. It was established that interband electron transitions play a dominant role in the formation of optical properties of the alloys. The research results are discussed based on new calculations of the electronic structure, which showed that both Co2NbAl and Co2VAl are half-metallic ferromagnets with full spin polarization as obtained from meta-GGA calculations. The half-metallicity of the alloys is shown up in their optical properties as a low free electron contribution (a decrease in the Drude-type absorption) and the intensive interband absorption in the IR spectral area, which indicates the presence of low-energy gaps in the electronic structure of the alloys.
Shreder et al. (Mon,) studied this question.