Internal exchange interaction of Tb+3 ions and influence of Si substitution on structural, electronic, magnetic and optical properties of YNi4Si -type TbNi5−xSix (x = 0, 1, 2) compounds

Abstract

We report the FPLAPW + lo study on new YNi4Si-type TbNi5−xSix (x = 0, 1, 2) compounds. The YNi4Si structure is a new structure type, which is an orthorhombic derivative of CaCu5 structure. The optimized lattice constants and internal cell parameters are in agreement with the available data. The calculated band structures show the valence band (VB) is mainly dominated by Ni–3d states in the energy range 0–4 eV below the EF, whereas conduction band (CB) by Tb–4f states about 2 eV above the EF. With the substitution of Si atoms for Ni, total magnetic moments decreases from 8.308 μB/f.u. (x = 0) to 6.052 μB/f.u. (x = 1), whereas magnetic moments on Tb+3ions increase from 5.92 μB/atom (x = 0) to 6 μB/atom (x = 1, 2) and the induced moments on Ni+2(x = 1, 2) ions decrease rapidly to a negligibly small value. Charge density estimates show that Tb-5d, Ni-3d and Si-3porbitals are mainly involved in bondings and there is a weak hybridization between Ni-3d and Si-3porbitals which varies with Si substitution. Furthermore, the complex role played by the Tb-5d1 electrons is also investigated, and found to be partly involved in metallic bondings as well as in intra-atomic charge transfer from 5d1 to 4f8 states. The calculated interband optical conductivity spectra reproduce the main features of the experimental spectra well and also reveal their metallic nature. Frequency-dependent refractive index, η(ω), the reflectivity, R(ω) and the extinction coefficient, κ(ω) for (x = 0, 1, 2) are also calculated for the incident radiation up to 12 eV.