Bismuth layer properties in the ultrathin Bi–FeNi multilayer films probed by spectroscopic ellipsometry

Using wideband (0.5–6.5 eV) spectroscopic ellipsometry, we study ultrathin [Bi(0.6–2.5 nm)–FeNi(0.8,1.2 nm)]N multilayer films grown by rf sputtering deposition, where the FeNi layer has a nanoisland structure and its morphology and magnetic properties change with decreasing the nominal layer thickness. From multilayer model simulations of the ellipsometric angles, Ψ ( ω ) and Δ ( ω ), complex (pseudo)dielectric function spectra of the Bi layer were extracted. The obtained results demonstrate that the Bi layer can possess the surface metallic conductivity, which is strongly affected by the morphology and magnetic properties of the nanoisland FeNi layer in GMR-type Bi–FeNi multilayer structures.