Influence of aluminum impurity on the electronic structure and optical properties of the TbNi$_5$ intermetallic compound

The electronic structure of the TbNi$_{5-x}$Al$_x$ intermetallic compounds ($x$ = 0, 1, 2) is calculated in the local electron density approximation with the correction to strong electron correlations in 4$f$ shell of terbium ions. Spectral properties of these compounds are measured by ellipsometry in a wavelength range of 0.22–16 $\mu$m. Frequency dependences of optical conductivity in the region of interband optical absorption are interpreted based on the results of calculations of electron densities of states. The relaxation and plasma frequencies of conduction electrons are determined.