INTERBAND OPTICAL-ABSORPTION AND PLASMA EFFECTS IN HALF-METALLIC XMNYFERROMAGNETS

The frequency dependence of the real and imaginary parts of the comple x dielectric constant epsilon(omega) in compounds XMnY (X = Ni, Pd, Pt , Cu; Y = Sb, Sn) having C1(b) structure are investigated in the spect ral range h omega = 0.05 to 8 eV. The values of conduction electron pl asma and relaxation frequencies omega(p) and gamma, respectively, are determined. The evolution of interband conduction and electron energy- loss function -Im (epsilon(-1)) for varying compositions is studied. I n all the compounds, apart from the main absorption band located in th e spectral range 1 to 7 eV, a low-energy (h omega = 0.3 to 0.7 eV) int erband absorption is revealed. An estimation is made of the energy gap at point Gamma of the Brillouin zone in the minority-spin subbands (d own arrow) for NiMnSb using optical data.