Interband Optical Absorption and Plasma Effects in Half‐Metallic XMnY Ferromagnets

The frequency dependence of the real and imaginary parts of the complex dielectric constant ϵ(ω) in compounds XMnY (X = Ni, Pd, Pt, Cu; Y = Sb, Sn) having Cl b structure are investigated in the spectral range ħω = 0.05 to 8 eV. The values of conduction electron plasma and relaxation frequencies ω p and γ, respectively, are determined. The evolution of interband conduction and electron energy‐loss function ‐Im (ε −1 ) for varying compositions is studied. In all the compounds, apart from the main absorption band located in the spectral range 1 to 7 eV, a low‐energy (ħω = 0.3 to 0.7 eV) interband absorption is revealed. An estimation is made of the energy gap at point Γ of the Brillouin zone in the minority‐spin subbands (↓) for NiMnSb using optical data.